Lillard is already 22 that hinders his ceiling somewhat ... he'll at least have some incremental growth going forward -- the biggest strides he'll take are probably just becoming more consistent. But counting on him to become a "superstar" (like a top ten guy in the league and in the conversation for MVP) is probably pretty slim.
I disagree with this premise. People said the same thing about Roy his rookie year, and before his knees went out he was a top 10 player. I look around the league at young guys who aren't in the top 10, and I don't see a huge list of players ahead of Lillard in terms of likelihood. He's certainly no lock, but I'd give him a 50:50 shot at it.
He's got a lot he can still improve on in terms of defense and shot selection and running an NBA team. Remember, last year at this time he was playing for Weber State. Nothing in his life has prepared him for the stage he's on now, and he's playing the hardest position to learn. He's succeeding now purely on shooting talent, instinct and a huge-ass set of brass balls. I think he'll improve a lot when he adds experience to that resume.