Hmm, I would like to see Hammerfell. Redguards, supposedly the best warriors in Tamriel. Resistance against the Dominion is alive and well in Hammerfell too which would make for an interesting story. Plus there's the huge desert....oh my, CAMEL MOUNTS
Black Marsh is supposedly inhabitable by non Argonians, or at least you'd probably die of disease and poisons. I imagine Black Marsh to look like Dagobah System for some reason.
Eleswyr, not my first choice but might be alright.
Summerset Isle, now that would be interesting. The very heartland of the bad guys to most people. The Island on its own would probably be too small though, but Valenwood is part of the Aldmeri Dominion. Maybe both lands to make a bigger game world? Just take a boat across or something. It would make a diverse world of f***f loads of trees and whatever Summerset Isle looks like.
On the subject of Akavir, I highly doubt they will make a game there. Yet. There's still history to be created in Tamriel. Another Great War probably, plus loads more mysteries. My guess is Akavir will be saved for a new Bethesda series, just like the Elder Scrolls games but set on Akavir, with completely new races. Perhaps some time in the distant future.
All of Tamriel for a TES game just doesn't seem right. Everyone's already explored Skyrim, and many Cyrodiil and Morrowind. I just don't see it happening.