My preferred theory, and naturally I am not the first to come up with the idea, is Hurt!Doctor is the Zeroth Doctor. The title of the episode "The Day of the Doctor" suggests that the story will be about how the Doctor got his name. This is the 50th anniversary special. One would expect it to be about the beginnings of Doctor Who in some way. The Doctor's pre-"An Unearthly Child" is essentially totally unexplored (and there are those such as Dr Sandifer who would wish it to stay that way) and thus is replete with unused potential unlike the Time War (how would a 8.5 Doctor fit in with the continuity of the novels and audios?). A Zeroth Doctor would ft better with what we see of Clara helping One steal the TARDIS. Finally giving the Doctor an origin story would set the programme up for the next fifty years. As an added bonus, if there were a Zeorth Doctor, Eleven has thus used up all his regenerations and Twelve can start again with a whole new set after various travails that can drive the Christmas special. (I remember talking to my brother about the regeneration limit after "The Deadly Assassin" back in 1976 and him reassuring me that they would come up with something when the time arrived.)
Yes, you're right, Hurt!Doctor will probably turn out to be 8.5 Doctor. If that happens, colour me disappointed. A Zeroth Doctor seems much more interesting and much more Moffat to me. Of course, with a bit of timey-wimey, Hurt!Doctor might turn out to be Zeroth, 2.5, 8.5, future and alternative Doctor. We'll know in two weeks.