They'd have to have an engine that does cloth physics first.
They'd have to have an engine that doesn't break in fourteen places every time an NPC blinks first.
Personally I'd like to visit Black Marsh for the next ES, or maybe the Summerset Isles. I've been intrigued by the Argonian homeland since Oblivion and the whole hist aspect and it would definitely be interesting to visit the home of the Altmer, considering the whole Thalmor situation.
Akavir would also be an interesting location to explore, stepping outside Tamriel might be interesting.