As far as what I think, I don't think he can be 'the guy.'
I think his ceiling is probably a better version of Tony Parker in his prime. A great PG, could be an NBA champion, even a possible NBA finals, but he's not going to be the top guy on the team.
Again, I think there's a really small pool of NBA PG's that you'd build your team around. I don't think Rondo can get to that very exclusive club.