On the one hand, I could see Moffat using the technicality of "so many Doctor's, but that's not really his name" as an excuse to play, because he's a devious SOB like that, on the other hand, I think he knows it would piss off the fans to much to change the order of Doctor's/ regenerations. Even if this isn't the Doctor, it would still take up a regeneration.
The idea is good, if he's going to swing it to the Time War, though, I'd much rather have had McGann as a manic, war-destroyed Doctor at the end of his tether.