If Cornwell doesn't win the job next year, I think it becomes an either or type situation. If Cornwell does win the job, and he proves to be legit on the big stage, the question becomes if he'll leave early or not, which could make room for Barnett.
I liked Cornwell a lot, but with the injury and what not he lost a lot of momentum. He's a bit like Coker in that both look the part, both physically are what you'd want, but that doesn't always translate immediately, if it did Coker would have been the starter because he clearly had the physical characteristics over Blake.
But... Barnett? He's the type of guy college coaches salivate over. He has the size, the arm, and he has the ability to run which can destroy defenses in college. It's kind of hard not to pull for him because of what he can do. Alabama hasn't had that do it all type quarterback really, someone who has size, speed, and a legit arm, it would be nice to see what Alabama can do with a Vince Young/Tim Tebow/Cam Newton/(Insert Ohio State quarterback here) type. I don't see him starting next year, I'd expect it to be Coker and if not Coker, then Bateman with Cornwell as kind of a dark horse. However, he'd have a great chance at the job the year after and I suspect the loser in that QB battle between Cornwell and Bateman might transfer.
