He's always been a PG. He's an explosive, quick, lengthy point guard with good court vision, shaky confidence and a terrible shot. Where that puts him in the league at the moment is as a serviceable but unreliable backup.
His future hinges on health, how his confidence changes, and whether he can improve his shot. His ceiling is still very high, but my fear is he'll end up like Burks where injuries delay his progress and he never quite "gets it". For example, Burks really needed to evolve his game somehow to become a great player and he just never did. Impossible to tell if Exum is going to go that route.