Actually, Matt Smith has confirmed he will be back for the 8th Season.
Matt Smith Confirms Himself for Series 8 2014 | Doctor Who TV
Of course, the question is, what is Hurt's doctor supposed to be.
Either he is a future incarnation of the Doctor, perhaps the one that becomes the Valeyard (A plot device from the awful Colin Baker years I'd sooner forget.) Or he is a lost incarnation of the Doctor from between the McGann and Ecceleston versions. The one that did the thing that wiped out the Time Lords and most of the Daleks.
I suspect that it's more likely to be the latter, but it presents a whole lot of problems.
First, it means the Doctor has only one incarnation left after this one before they have to pull some kind of plot device out of their butts to explain why he gets more than the alloted 13.
Second, if this "Evil Doctor" was the one who killed the Time Lords, why has he suppressed it? In all the other dialog, he seemed perfectly at peace with what he had to do to his own people to keep them from destroying all of creation.
Third, we've seen the Dalek's files on The Doctor up to Tennet's incarnation in "The Next Doctor" (where Jackson Lake downloaded it into his brain and believed he was the Doctor.) You think this guy would be pretty important in that file.