I imagine they'd keep the original ten. What else could be added? The Dwemer are long gone.
well there's the Maormer (sea elves) that used to live on summerset isles, but were exiled to pyandonea.
then there's the Imga, a race of quite civilized Ape men from Valenwood.
But the fact is, we can't predict if that keep the same 10 races, or if they substitute any new ones in. There's an almost 200 year gap in lore that we don't know about, so you never know.
I mean its definitely plausible to think that maybe Argonian's aren't playable. That's just an example, (dont freak out at me) but last we know, the Argonian's ceced from the Empire and invaded Morrowind. If we're supposed to be working with the Blades (who last time i checked were pretty adamant about preserving the Empire) , why would we be able to be part of a race that hates the empire? Again, just an example, food for thought.
until we get more information on the time between the infernal city and skyrim, we have no way of knowing.