Well, Damon Lindelof has given an interview about the next movie, and he's being very uncharacteristically direct for Abrams & Company. He says, straight up, that they have a plan for the next movie and that it involves the Klingons. He also says that they would be "incredibly stupid" not to use Benedict Cumberbatch again. So I think it's fair to say at this point that the current plan is to see both Khan and the Klingons in the next film.
Lindelof also goes on to say that two of his favorite adversaries from the Trek universe are Q and the Borg and that he would like to see them. But he says that's farther down the line, "towards the end of our run on Star Trek
." That statement, to me, implies two things: First, he sees their run on Trek extending beyond the three films and, second, that after they do the Klingons, they're likely to do Q and/or the Borg.