Never too soon to start fighting about the next one.
I can't decide whether they're more likely to leave Khan alone for one movie and focus on something like Klingons, or whether Cumberbatch is just too irresistible now that he's been set up.
Probably the latter, given that they're going to rely increasingly on foreign box office after this and now that he's revealed they can use Khanberbatch more explicitly to promote the film. People are saying that not being able to focus on the villain during promotion hurt this movie (arguable, I think) and what's better than a familiar villain folks recognize?
Marla McGivers is still out there somewhere. Bets that she's involved in the next one. Probably works at the cryonics facility.