So I'll start?
Well, I think it's obvious that it's extremely difficult, if not impossible, to produce any consise list of Pillars for Legacy. They have actually done (I'm not counting the Mystical Tutor banning that has yet to go into effect, as I think that's a mistake) a very good job of creating a healthy and balanced meta, with a very wide variety of decks.
Part of the problem is the definition of "Pillar", in fact, in
Crafting a Vintage LaPille actually didn't use the term in this crucial paragraph (or in the entire article):
In the modern era, we have a more nuanced understanding of the Vintage metagame. The four tournament Vintage archetypes that we have identified revolve around four cards: Dark Ritual, Force of Will, Bazaar of Baghdad, and Mishra's Workshop. In the current Vintage metagame, Mana Drain is by far the most powerful unrestricted blue card other than Force of Will, so almost all of the Force of Will decks are also Mana Drain decks. In order to keep a diverse metagame, all four of these archetypes need to have a real shot at winning a match and the archetypes need to stay distinct.
The most immediate definition of 'Pillar' we can get from the above is "a card around which archetypes revolve".
In Vintage some decks make use of more than one Pillar, the examples that come to mind first are TPS, which uses both Force of Will and Dark Ritual, and Welder-Shop-Bazaar decks intending to use the graveyard as an extension of the hand. (Please note that I have made arguments against Force of Will being considered a pillar, a minor consideration of which is that Mana Drain + Dark Ritual decks are far more rare than Force of Will + Dark Ritual decks (almost by definition, since Mana Drain's presence indicates with very high likelihood Force of Will's presence.) That would I think be an inevitable outcome of establishing Legacy Pillars.
In any case, in Vintage the Pillars each support multiple archetypes:
Dark Ritual supports TPS, ANT, and mono-black decks like Dark Times, among others.
Force of Will supports a wide variety of decks (which is partly why I personally don't think it's useful to name Force the Pillar), including Oath, Fish lists with blue, Mana Drain decks, etc.
Mishra's Workshop supports MUD and 5C Stax.
Bazaar of Baghdad support Dredge, Madness, and some Stax decks also abusing Goblin Welder.
These short lists are not meant in any sense to be comprehensive. TMD has whole forums to the discussion of decks based on these pillars (but don't go in the Null Rod forum, because Null Rod isn't a DCI recognized pillar!).
Legacy has many linear archetypes, best exemplified perhaps by Tribal decks, which I think pose a particular problem to establishing Pillars:
Goblin Lackey is an extremely powerful card... in the context of other Goblin cards worth cheating into play, and the ability to connect with him.
Lord of Atlantis is a strong creature considering that there are other Merfolk creatures worth playing, and that Islandwalk and additional power/toughness are good things for them to have, etc.
Neither of these cards enable multiple decks though, just their own dedicated decks. Unless we expand the definition of Pillar to include tribal synergies, the closest I think we can come with such decks to one particular card is: Aether Vial, though not all Goblin or Merfolk lists play Aether Vial.
Legacy also has a variety of control strategies, the most prevalent of which are Counterbalance-based. Counterbalance supports a variety of decks, including Natural Order Bant, and Thopter Foundry-Sword of the Meek combo decks and others.
I don't have the detailed knowledge of the Legacy metagame, or the chops to definitively recognize Legacy Pillars. I would guess broadly that Tarmogoyf, Life from the Loam, Tendrils of Agony (or potentially LED, which would allow us to lump in LED-based Dredge), and Entomb qualify. Noble Hierarch and Survival of the Fittest are contenders for Pillar Status as well. I also haven't mentioned one-off decks like Enchantress and Non-LED Dredge since there aren't recognizable (to me) cards those decks 'revolve around'.
Part of the problem is that the best cards in Legacy aren't as different from one another so as to distinguish archetypes, while retaining variation within each archetype. This is a problem best exemplified by Tarmogoyf, which 'goes in everything'. Tarmogoyf is worth protecting, so it goes in Counterbalance decks. Tarmogoyf is better (in some people's opinions) than additional Merfolk synergies, so it goes in Merfolk. Tarmogoyf is likely to be in play for your opponent, so playing one alongside Noble Hierarch allows yours to win in battle. In Vintage, Force of Will (and to a greater extent, Mana Drain) is extremely strong, but also has strong disynergies with Mishra's Workshop (which powers out cards that make it hard to play Force for its alternate cost, or pay
for Drain), and Bazaar of Baghdad (at least in a Dredge context, and speaking historically, as Force has crept into Dredge). Vintage obviously has a host of cards that 'go in everything'; the fast mana that are at times preferable to lands: Moxen, Mana Crypt, Sol Ring, and Black Lotus. Decks intending to pay mana for non-artifact spells generally find room for other extremely powerful cards, such as: Ancestral Recall, Time Walk, Demonic Tutor, and Yawgmoth's Will.
[Some argument about how Legacy lacks a core of super powered cards relative to the rest of the format, and lacks a second tier of disynergistic cards capable of supporting distinct archetypes. To a much greater extent in Legacy as compared to Vintage whole archetypes are just singular decks with next to zero internal variation.]
This is clearly rambling, and I've spent all day so far writing it off and on, so I'll just put this much out there now, and get back to it again later. If anyone wants to take what I've written so far and run with it, have at it.
