I really think that the answer that will be revealed in "The Name of the Doctor" will be something along the line of "I don't know".
I think that the Doctor doesn't know the answer to the question of "Doctor Who?", and doesn't particularly want to know. Is in fact, actively fleeing/hiding from the information for some very important reason. (Like when 10 was hiding his Timelordiness in "Human Nature / The Family of Blood".)
When he silenced Clara before she said his name aloud in "Journey to the center of the Tardis", he didn't seem all that concerned that she knew his name, but that she not tell him
what she knew, because he has blocked this info from himself for some higher purpose.
The revelation that Moffat promises we'll come away with, is that not even the Doctor knows who he really is, and the why of this will form the underlying theme of the next series.