IMO, there is just no chance in hell that he will leave early. He has got it made right now, in an absolute ideal situation in college. No reason to leave that behind, he is a lock to stay 4 years.
I think he will end up being a late 1st-early 2nd round draft pick. His name will be too big to not to be drafted. Whether he makes it in the NBA will depend on his defense and shooting. He will have to carve out a niche by playing defense and making jump shots, because he wont be able to play the way he is right now in the NBA. His size is the main issue for him, if he was 6'10 he would be a top 5-10 pick. Doug is such a unique player, I don't know if there really is an apt comparison out there.