All depends on whether he beefs up his serve. If he continues with his petit delivery, I don't see him improving much. If he comes out blazing in 2013 with a stout serve, I can see him knocking on the door of the top 10 throughout the year.
If he manages to beef up his serve, he will make it to the top 8 easily. He already beats Ferrer, Berdych and Tsonga more often than not while virtually getting no free points on serve. If he could improve his serve to a decent level, he'd be a much stronger contender for sure.