I think they should have Falmer actually reappear as a race. I'm tired of these long dead elf races that vanished (there's never any long dead human races in these games); they should have the Falmer returning as a twist.
I doubt any new races will be playable, but if it takes place in Skyrim I wouldn't be surprised if we get to learn a lot more about the Falmer, and possibly even come across what's left of their descendants. I think it's possible that they incorporate them as DLC at least...
The thing is, they need to make the game world much bigger to make something like that credible... I mean, most ES sites will acknowledge that their may still be Ayleid tribes living deep within the jungles/forests of Cyrodiil . . . and yet in Oblivion, there AREN'T deep jungles or forests... And the whole game world is only a few miles across. In a world like Daggerfall's -- not that I think it's fair to ask for them to try to do something like that again -- you could definitely get away with placing the last Ayleids out in some remote corner, miles from civilization.
If TESV takes place in Skyrim, I'd like to see a noticeably larger game world. With today's technology, it's very possible to make vast worlds without sacrificing the "living" quality you get from smaller, more "hand-crafted" worlds. Look at Just Cause 2 for example . . . over 1000km
2. And the graphics are amazing too! I'm not asking for or expecting that, but I sure wouldn't mind a world that's around 100mi
2... It makes things like the Falmer idea a lot more believable. Because really, you're not going to wander from a major city for just a few minutes, and suddenly come across a long-lost culture chillin' in an undiscovered cavern, and surviving without making contact with the rest of civilization. It just doesn't make sense... Even if the inhabitants didn't leave the cave, other people would stumble across it.