I would think that the djinn would have some influence here. I don't think we'll see what Dean *really* would have been like, only what the Djinn will twist his reality into. Djinn are supposed to resent being made to give wishes, and in most stories, seem to try to find ways to make the wisher's life more miserable than it was before he started making those wishes.

(Although you'd think Dean would know that...)

I hope they make that obvious though, because I think the man we see would have turned out to be good with strong convictions and a strong sense of right and wrong, no matter what his upbringing.