I think a tileset that we've never had anything close to, is a proper Elven City. Something from the Crown-Wars era, when elves covered the earth and all those ancient elven ruins you see in modules today were, you know, not ruins yet.
The closest thing we have is a reskinned underdark tileset to give everything a treebark texture, which really doesn't convey the majesty that I'm thinking of. Elves built with stone, and metal, and made lovely things like this:
...And it's a shame there's nothing like that on the vault.