I really don't think this will be good enough for inclusion in most decks. Fetching into fix mana and duals seems a lot better. Breaking two of them via the legend rule doesn't really warrant inclusion either since you need to have two of them in hand for it to do anything that a basic plains can't. You can't fetch these things out, and you're not seriously going to run tutors to find a second one of these to break.
This is better than a basic land (and I'm assuming there is a whole cycle, 1 of each color).
If you are playing WW, why not run this? It acts as a fetchland and basic land rolled into one. Just put 2 in your deck to cut down on the chances of having a dead land card (or 4 if you want to fetch out extras).
It 'gets around' strip effects by replacing itself when it hits the graveyard.
Assuming this is a cycle, the blue one should be an auto include in most every T1 deck, even as a single copy.
It basically reads:
Polluted delta - Legendary land Tap: U
With a Green one, think of Vinelasher kudzu, crucible and fastbond.
Granted, it may be useful to a White Weenie deck, but it would take a lot more than a cool land to make WW a legitimate vintage deck in the current meta, and I highly doubt it could be used for anything else since the only upper tier decks that really run basic plains in multiples are fish and bomberman, and they like their mana bases stable and full of lands that either fetch when they want them to for access to different colors (nope, and the plains comes into play tapped), can produce more than one color (nope), or are basic for protection vs strips and are fetchable (nope, and again subpar strip protection as the land CIPT).
Not to mention the tempo hit you'd take by legend ruling them out. Tap Flagstones for W, play second flagstones, legend rule them off, grab 2 tapped lands. So if you grabbed 2 basic plains, you can tap for W that turn and put a plains into play tapped. Not so good. And even if you went for a pair of white duals or a combination of plains/white duals, you basically thinned your deck a little bit and played an Invasion tap-dual. Still not so good.
Also, there is unfortunately no cycle of these, the spoiler confirms 12 out of the 13 nonbasic lands in the set already and Flagstones is the only one of its kind.
