Well, they've already done Morrowind, Cyrodiil (Oblivion), Skyrim, and High Rock and Hammerfell (both in Daggerfall), so it would be nice to see them set a game in the Bosmer/Aldmeri, Khajiit, or Argonian homelands.
Summerset Isle, maybe Elsweyr. Honestly, it's a bit of a gamble setting a game in a world where the majority of NPCs are not going to be human (or at least elves). There's only so much 'Khajit has wares for sale' and 'This one believes you are trying to swindle them' you can take.
These games cost so much money to make now that they can't afford the setting putting people off. Skyrim was a very safe bet. A desert or weird swamp? Not so much.