Honestly, I think Bethsoft should stick to what they know and do best. Gimmie a sandbox in Akavir. I mean, what are options for new provinces in the next Elder Scrolls? The only one that sounds even remotely interesting is Hammerfell, and that's if you don't count Redguard's centering around Stros M'kai. The only other ones we've got left are Black Marsh, Elsweyr, and Valenwood...dunno if the Orsimer have their own little state or whatever. Black Marsh would be dull as fuck because wandering around every day in a mosquito-infested shithole of a swamp isn't exactly my idea of excitement. Elsweyr might be a little interesting, but if memory serves, its largely a desert area and we've already got massive deserts in Fallout. Valenwood is full of elves, and the less said about that, the better.
Besides, we've spent five games, not counting spinoffs and expansions, in Tamriel. If you didn't bother reading the books in the game, you'd be forgiven for thinking that it was the only landmass on the entire planet. Hell, if you wanted to, you could throw a bone to the hardcore Morrowind fans and make it so your character is actually the Nerevarine, since the Nerevarine is confirmed to have made a journey of unknown success to Akavir prior to the events of Oblivion. It'd be a perfect chance for a direct callback to a previous installment and give us a chance to see an entirely new land. They wouldn't even have to stat any new races for player characters, so that'd make it that much easier.