He is too light in the arse to play the 5 and does not have the skills to play a 3...so he'll be a 4 with mostly an open floor game and limited defensive skills (although he can and does block shots well). The thing I don't think he will ever have is skills to drive the ball - he'll be a spot shooter, open floor runner, play above the rim guy....that gets pushed around in the box. I don't think he can be a starter any time soon if ever - but the NBA will pay you alot of money to ride pine and attend practice.
He was a 6'2" guard as a freshman. He has decent ball handling skills, he can drive, and can shoot from 3 pretty well, CU just didn't want or need him to do too much of that. He grew late, which is why he was a fairly unknown until late in his high school career. I don't think anyone expects him to play the 5 in the NBA.
Your concerns about him getting pushed around in the box were some of the same concerns that people had about Kevin Garnett, and he played 21 years. Mikki Moore had a decent NBA career. Both were built like him. I'm not going to say he'll be another Garnett yet, but I certainly think he will be no worse than Moore.
The latest mock draft I saw showed him going to Denver with the 14th pick. In today's NBA, he will play. 30-40 years ago?????