There's plenty of reason for optimism. He has a good chance of improving his shooting from 3 which was already OK. He was never 100% physically last year and may be more explosive going to the hoop when fully healthy. And, it's reasonable to think the game will slow down for him and he'll be a better playmaker...that happens for many guys at his age.
If he does all these things he'll be one of the better young guards in the game, considering his elite defense. And, all of these things are part of the normal progression for young players...it's not like the "maybe Jeff Green will start to consistently score like a #1 offensive option" discussions from a few years back, where people were hoping a guy would totally change his DNA as a player, at age 26.