One thing that I never liked is how they "dumbed down" Skyrim as someone said it, I felt like Skyrim lacked a lot of content compared to Oblivion and Morrowind. One thing I missed in Skyrim more than acrobatics, was attributes.
That being said, they seem to like to change it up a bit with their areas. Morrowind was a desert (for the most part), Oblivion was a woodland (for the most part), and Skyrim was a snowy waste (for the most part). That leaves the Jungles of Elswyr, Dragonfell mountains maybe (kind of like skyrim wihtout snow?), possibly the wood elf realm Valenwood (depending on the type of woods). Honestly for the most part, I want to see the Summerset Isles, that would be an interesting place to see.
No matter what setting they choose, I hope they at least go back to their roots and not dumb down the game. At least it's unlikely we'll have gunpowder pirates sailing the seas as our next game.
They can make a new TES covering Akavir where Nerevarine has went probably. There they got real serpent/snake races so why not skip Black Marsh.
Or we can play during first era as the Empire rises, possibly first war against the Akavir? I'd find that an interesting game.