I've been running a list similar to what's been posted. So far I've mostly been testing in the TP room. My list includes Demonic Consultation (it's an absolute beast in a deck with multiple 4-of,) and I also use Yawgmoth's Will.

Two notable matches (match-ups which I've historically had difficulty when piloting other decks)

2-1 vs. Dredge
Lost game 1 pretty quickly, couldn't assemble anything. Games 2 and 3 were much easier. Leyline of the Void from the board slows them down tremendously. I've noticed that the dredge meta (at least online) has morphed to include the depths/stage/hexmage combo from a transformation board. Shops-depths is more redundant and more resilient, and we're faster at assembling depths compared to dredge doing it from the board.

2-0 vs. Storm
A combination of lodestone and thorn in both games locked the board enough for me to assemble the combo. Again, Leyline from the board is a powerhouse card. It completely nullifies the utility of dark petition. Both games played out in a similar fashion. Thorn/golem slowed him down. He cast some number of cantrips and durdled a bit with a top. I dropped Revoker naming Lotus (hadn't seen it yet, anticipated it would arrive.) Next turn I assembled the combo and passed. He attempted to ancestral, I had misstep. He misstepped in response. At EOT I got Marit Lage, he attempted to Chain of Vapor. I used Demonic Consultation to find another misstep. Won next turn.

The deck is a blast to play. Very dynamic, despite it's linear appearance.

I've been brewing a UW deck based off already existing grindstone decks. The deck can win with through painter/grindstone, vault/key, or tinker/bot. I enjoy it quite a bit so far, and I've had moderate success battling against Mentor.

I run a still-in-flux number of Supreme Verdicts (right now it's 1 main, 1 side.) It's nice. Also, I'm running two additional sideboard answers which help to slow the game down enough to at least allow me to process lines of play: Lightmine Field and Circle of Protection: White. The Lightmine Field has been OK in testing. The opponent usually just grows the token army over a couple turns and then goes for an alpha strike. However, the Field buys me a couple turns to construct my combo (painter/stone is my preferred route, and it's extremely compact.)

Circle of Protection: White has been another option to slow down the game, and it's quite good at that function. Eventually the opponent gets enough tokens to go wide around my ability to pay for the enchantment's ability, but it serves a similar purpose to Lightmine Field: slow down the game and buy some time.

I'm still deciding on other possible sideboard cards. Lately, I've been expanding my field of view when choosing cards for decks.  There are hundreds of cards which I might have never played before, but I'm willing to experiment and see if something works. At the very least, it's fun playing niche cards in vintage.

As a final note, one spicy maindeck card I use is Meddling Mage. I name Monastery Mentor, and they dig furiously for an answer. The opponent usually has several answers to find: Bolt, StP, whatever else. But I also run a full counter suite which helps protect the Mage. Again, it's just another option I'm testing out.

I run 3x Thirst. I cut mystical tutor and Gifts to make room. I also run Goblin Welder, but I'm not sure how much I'm liking it so far. In my testing (numerous matches in Tournament Practice, and some 2-man queues,) every time I could cast goblin welder, I wanted to do something else instead. Plus, in many match-ups welder either doesn't make it to the battlefield (misstep, et al.) or gets burned/bounced/StP. I'm considering putting Welder in the sideboard and bringing it in when the match up is more conducive.

I've also seen some lists running a counter package (force, pierce, whatever.) I'm still running a 3-1 Defense Grid split (3 main, 1 board.) Steel City has always been about jamming multiple threats in rapid succession. The threat density is high enough that the deck can eschew typical protection. I'm very aggressive when I play Steel City. I'll play anything until it sticks: Defense Grid, Thirst, Wheel, Timetwister, Key/vault, some tutor, Windfall, Wish for something, etc. I tend to choose lines of play quickly and just jam threats repeatedly. The play style can be a bit jarring for the opponent; they're always reacting to something.

To bring this full circle, I've been enjoying unrestricted Thirst. It's an all-star and it typically over performs.

I've been trying the Defense Grid/Discard package. I like it much more than the counter package. I currently run 3x Defense Grid and 3x Discard (duress/thoughseize) main. My SB contains 1 additional Defense Grid and 1x Thoughtseize (an option for Wish.)

The online meta is blue/counter heavy, and Defense Grid is a must-answer card each time. I had a match last night in Tournament Practice in which I had 2x Defense Grid (opening hand, natural draw). The opponent FoW both and then he was basically top-deck mode. I didn't even need the Defense Grid on the board; they served an alternate purpose (eliminate countermagic threats.) I eventually won with vault/key.

I think it makes things a bit wonky. There are other 3-drops that I'd rather cast over chromatic lantern (wheel, tinker, twister, thirst, etc.) Under pressure from thorns and spheres, I'm more likely to cast an immediate bomb over chromatic lantern.

I've been in matches against MUD where my Seat (or City) gets hit by wasteland, and I'm under pressure from thorn and sphere effects, and/or a revoker is named on Chrome Mox (or some other mox.) I've come out from under that pressure by carefully sequencing my spells and turns so that I can either a.) Wish for Shattering Spree (or sometimes Vandalblast,), or b.) build up enough artifact acceleration and Hurkly's them.

In all of the matches I've played against MUD my immediate plan is to pump out as much artifact acceleration as possible and then Hurkyl's or Wish + Shattering. Under a chalice@0, I have to carefully sequence land drops to be able to cast Hurkyl's.

However, there are some scenarios against MUD that present a game that I cannot win, regardless of my hand. A board state of Lodestone + Chalice@0 + 2x Thorn effects + Wasteland is an excruciating lock. The deck is not designed to beat every possible permutation of MUD decks. It is, however, capable of overcoming the pressure via Hurkyl's or Wishing for the appropriate answer.

MUD is not an easy match-up on the draw, but it's certainly not un-winnable. In all of the scenarios I mentioned, I don't see chromatic lantern + Citadel changing the landscape enough to warrant their inclusion.

Steel City has been a favorite deck of mine on MTGO. My list is similar to other lists posted. I run 1x Tezz. Inkwell is my creature of choice (seems better in the online meta.) I enjoy this deck because sometimes I like to run 1-of cards that I enjoy. For example, I use 1x Chromatic Sphere from time-to-time.

We've all just started dipping our toes into the water. As we take our decks to various tournaments (Online Dailies, local tournaments, regional, etc.,) we'll continually refine our lists. I believe we have seen some very solid lists, and they will only become stronger over time. The meta will adapt if necessary, but then Gifts pilots can adapt in turn.

I've shared this sentiment several times: Gifts decks are resilient, reliable, and versatile. I'll add adaptable to that list. It is my opinion that the best is yet to come for Gifts decks.

I feel comfortable with the following configuration for handling hate:

Main deck:
1x Ancient Grudge
1x Nature's Claim
1x Repeal

SB:
4x Ingot Chewer
2x Nature's Claim

I run 2x Tropical island main (to support Fastbond, regrowth, etc.) So I can easily bring in both Nature's Claims for games 2 and 3.

Also keep in mind that the main deck runs 4x Mental Misstep.

EDIT: And to the point of other Gifts brews: Yes, I agree completely. It's worth testing a variety of Gifts decks. I've been tinkering around with Ritual Gifts storm (3x Dark Ritual, Necro, Bargain, Timetwister, et. al.) and I like it. It's more explosive than Control Gifts (UBx), but less resilient than the list that Stephen posted.

In Game 1, against an unknown opponent, I would anticipate that most of my Gifts piles would be heavily reliant on the graveyard. Isn't that the point of Gifts piles? Select 4 cards with the intention of being able to play/cast/recur all of them.

Main deck Ancient Grudge (or nature's claim, or whatever,) is a very easy and fluid adjustment to make.

Grave hate is a problem in every meta (Cage, et. al.). I don't see why that should dissuade us from going for graveyard-intense Gifts piles game 1.

If all of my opponents in my meta were maindecking 3-5 pieces of gravehate (going whole-hog hate for game 1,) then I might adjust the deck list. As it stand, people aren't packing that much graveyard hate game 1 in my experience. Furthermore, the sideboard exists for a reason. You know, game 2 and 3.

I'm perplexed by the knee-jerk reaction that this list folds to X, Y, Z. Please build the deck and try it, in various iterations, with varying splashes to suit your liking. I promise you the deck is highly resilient and utterly consistent.

I've been testing a similar list online (with green splash) and it's consistent, fun, resilient, and reliable. A large percentage of my Gifts piles contain one (or both) of Snapcaster and Noxious Revival. Both cards offer tremendous resiliency in any situation.

Finally, Ancient Grudge is great main deck (I run 1x Tropical main.) Grudge in a Gifts Pile is amazing. Sometimes it's a single spot removal; other times it's a double-dip (cast from hand, then from GY.)

I've been testing a similar shell. However, I modified it by I adding in the Gush-Bond engine. I did this by making the following changes:

-2 Thoughseize
-1 Abrupt Decay
-3 Fact or Fiction
-2 Jace, the Mind Sculptor
-1 Mana Drain

+1 Mental Misstep
+4 Gush
+1 Fastbond
+1 Gifts Ungiven
+1 Preordain
+1 Regrowth

I've always loved Fastbond. I use it whenever I can. It feels natural in this list, because a.) It helps to hasten the resolution of Gifts Ungiven, and b.) Gush-bond is a nice engine and alternate path to victory.

I've also been testing a Gush-Bond storm version of the deck. It has two divergent victory conditions (Tendrils, or vault-key.) That list uses x3 Dark Ritual. I can't recall off-hand the entire list. I'll post it later if I remember.

There are so many possibilities, that it's worth testing various Gifts brews in different combinations of colors. I do like the idea of a white splash. Balance is always a nice card to add to the Gifts pile, especially if they're on delver/pyromancer. I envision a pile of [Balance, Time Vault, Key, Noxious Revival.] They're forced between giving me access to combo pieces, or they can choose a board wipe. I'd probably choose this option if I had something else in hand to recur a combo piece or tutor for another wincon after Balance (tinker -> bot.)

At the present moment, my testing has revolved around BUG Gifts lists with red splash (for recoup -- not sold on that yet.) But, I'm eager to try a white splash (Balance, swords, enlightened tutor, or whatever else I can think of.) Of course, I could also try 5c and use Burning wish, but then I think the deck is diluted by trying to do to much. A solid combo Gifts deck with control elements is where I'm leaning.

I'll be doing additional testing for WUBG Gifts (splashing white for Balance.) I'm going to use both Noxious Revival and Regrowth. Both cards have so much utility.

That's a very broad statement. Your tinker target of choice depends on many factors, meta included. When playing MTGO I prefer Inkwell. I seem to run into a lot of exiling shenanigans and bounce.

Which is what brought me to my third point in my post above: The power of Gifts lies in the game's brevity after resolution: If you build the proper pile, you'll win. I was contrasting that with the need to do other value-added plays after a single DTT, because often a single DTT won't win the game (at least not as effectively as a single Gifts.)

I prefer Gifts over DTT (in specific lists, not all lists) for a few reasons

1.) Back-to-back Gifts are recursively effective, whereas back-to-back DTT are difficult to cast (sometimes, not possible at all.)

2.) Repeated Gifts have added value because you'll be choosing from a smaller card pool and you can further fine-tune your successive Piles to be even more effective. Repeated DTT have diminishing value because a.) As in point 1 the graveyard is smaller and a second DTT might not be possible, and b.) If you've cast 2 DTT to get 4 cards you need, you've done so from size-neutral library (DTT puts unwanted cards back into your library, not into the graveyard), but 2 Gifts would have given you 4 cards you need/want from a single spell (if you've built the proper pile.)

3.) Sometimes, a resolved DTT can win the game (if you already have other cards you need), but more often it will enable a win by setting up the proper combo. A resolved Gifts, however, usually wins the game immediately if the pile is formed strictly with the combo in mind (i.e., there is no hate to combat.) Under duress of hate, Gifts still has an upper hand because the type of hate that hampers Gifts will most likely hamper DTT also (resolve it through sphere effects, access the graveyard, etc.)

I've been testing (in Freeform on MTGO) my Gifts brew. It's been working out quite well. I make changes to the list daily, so I can't post a definitive deck list. But, I can say a few things about what I like (and what I don't)

1.) I run 1x Noxious Revival and 2x Regrowth.
2.) My primary wincon is vault+key, secondary is tinker -> inkwell (in many matches, I prefer Inkwell especially if the Monastery Mentor + STP deck takes flight.)
3.) In Game 1, my Gifts Pile is usually [Time Vault, Key, Noxious, Regrowth]. In Game 2 (in the face of copious grave hate, my Gifts Pile will be some variety of [Abrupt Decay, Demonic Tutor, Tinker, X], where X is a flex spot that depends on additional hate and the board state.
4.) I've been liking my BUG version of the deck. I play Abrupt Decay and some number of Deathrite shaman.
5.) This is the most important point of my testing, and I'm still undecided: I usually run 2x Dark Ritual. It helps to power out a quicker Gifts. I don't know if I'd run only 1, and 3 feels superfluous. Regardless of how many I run, I'll board them all out in Game 2 against Shops.

Gifts is high CMC (especially for vintage,) but when you're spending 4 mana to potentially win the game (on turn 2/3 with good acceleration,) it's fine I think.

I'm brewing lists with 4x Gifts, and some number of deathrite and abrupt decay. I can handle Grafdigger and there's enough filtering/tutoring available that I should be able to craft a win without gifts (tinker inkwell), or craft a win with a proper Gifts pile.

With enough recursion and draw effects, I think 4 Gifts is a good number (but I might end up with 3.) Gifts followed by another Gifts (next turn, or whenever,) is a fun sequence. The first pile can be strategic and the second pile can be a fine-tuned win package with 2 or 3 enablers depending on the win condition. In my testing, I've never been upset to have multiple Gifts.

I've also had a few matches where I have 2 vengevines in hand and LED has helped tremendously in that situation.

Let's suppose the mana I have is G (forest, or tropical, or whatever) + LED. I can use G to discard the first Vengevine, hold priority to crack LED (discard the extra vengevine), then with GGG from LED find/discard Vengevine, Vengevine, Rootwalla, Memnite. I'm searching for 4 creatures with survival, but the first creature is found from the discard trigger of the initial vengevine. Also remember that rootwalla is cast for madness, and memnite ends the chain so it's free.

If in that situation I had G + Black Lotus instead, I would only be able to get 3 vengevines (because if you have two in hand, you'd need GG to discard both rather than a "free" discard from LED activation.)

The difference between 3 or 4 vengevines is minor in most cases, but an extra 4/3 is always beneficial.

I've been running a similar deck online, and I'm enjoying it. I use a Chrome Mox and I also run Lion's Eye Diamond. On the turn when I'm chaining survival discards, simply hold priority (hold ctrl while activating survival) then crack LED while the discard trigger is on the stack. It's great when your hand has chaff in it; it's effectively a black lotus.

I'd like to specifically look at Delver decks (although I think Trespass can find a home in other viable decks).

I'll use a metric that I'll refer to as "graveyard value." Consider the following two antithetical scenarios:

1.) A graveyard with 8 fetchlands (highly unlikely.) This graveyard has a low value.
2.) A graveyard with 8 cards that are a mix of burn/cantrip/creature (killed or discarded, or whatever.) This graveyard has a much higher value than the first scenario because a.) the presence of burn/cantrip means that you should have some card advantage, board advantage, virtual advantage, etc., and b.) you've cast meaningful spells that have impacted the game state and have brought you closer to your endgame (i.e., critical mass in Delver/pyromancer)

I think Trespass is very good when your graveyard has high value. If you would have cast a Time Walk in that scenario, but you instead only have Trespass, then Trespass is just as good because your extra turn will probably win you the game. Remember that a high-value graveyard means that you probably have an established board presence and have impacted the game state in a positive way. If a Delver player only needs to Time Walk and win, Trespass will serve the exact purpose and both spells would have equal value when the graveyard is high value.

Let's look at a scenario when you have some number of cards in hand that include both a Treasure Cruise and either Trespass or Time Walk. If you Cruise, then the value of your graveyard is depleted and the value of Trespass is also lowered. A turn that is Cruise + Trespass is very resource intensive and also implies a late game line of play (UUUU + 15 cards in your graveyard.) If you have all of those resources available then the game is long and the extra cards would have more value than the extra turn, further depleting the value of Trespass. If, however, you have Cruise + Time Walk in hand, the value of Time Walk is just as strong as if the graveyard had low value, and its value is not depleted by Cruising first.

I would propose running 3 or 4 Cruise + Time Walk + 1 Trespass and cutting another delve card somewhere (DTT if a build is using it, or Cruise if the build has 4.)

I've played a similar deck on MODO and I'd suggest this:

-1 Gifts Ungiven
-1 Cabal Ritual
+2 Chrome Mox

-1 Thoughtseize (move to wishboard)
+1 Hurkyl's (move to main deck)

-1 Badlands
+1 Mana Confluence
For the mana base, I've been a huge fan of the full complement of rainbow painlands (city + confluence.) Your mana base might provide more durability, however, especially if you land an early Necro or Bargain.

Finally, the deck is capable of generating large amounts of mana very quickly. Have you considered Vandalblast in the wishboard?

I've been play-testing with a similar build, and I always enjoy using Gifts Ungiven. It's quite versatile and you can adapt the pile based on the board state and what is in your hand. Sometimes I'll include Reconstruction in the pile. It's a niche card that interacts quite nicely with the deck.

Another card I enjoy is a singleton Chromatic Sphere. It's mana + draw when needed, or it's a transmute sacrifice + draw when needed.

EDIT: I've recently tried the deck with some modifications that people suggested above. I'm using 2x Goblin Welder, and I switched Gifts to Fact or Fiction. The deck operates as a mix between your deck and Steel City Vault. I highly recommend you add the Welders. They offer phenomenal synergy with most of the deck.