I think there's little doubt in any of the coaches' minds that JP is the starter. Because of Nall's injury, we just haven't seen enough of him and he hasn't had enough time in this offense to seriously consider him to start opening day. Even if he plays the whole 1st half of the 3rd and 4th preseason games and plays well with the starting offense against starting defenses, in my mind it still wouldn't be enough to hand him the job over Losman.
However, I do think he should start and play the whole 1st half of the next game, for the purpose of deciding whether he's ready for the backup role. I suspect he'd show more than Holcomb has shown us this preseason and win the backup job right there. And, in these days, rarely do starters take every snap in a season, so in the backup role Nall will eventually get his shot.
It's amazing that he was the better half of his team with Don Criqui.