I see Wallace as the player that most likely poses a threat to Coach Stevens. (Still can't believe the Celtics' coach is a guy called "Brad Stevens".)
He's a guy that plays the position that the second best (arguably) player on our team - Jeff Green plays, has been in a lot of NBA situations, and has zero future on the team. It's easy to imagine him both having an ego, and thinking he knows better than some young coach with no NBA experience.
But, on the other hand, Stevens is going to have to learn to deal with players like that - and Wallace is not a very important player. So if they end up having problems - whatever Wallace says doesn't matter much.