There are a few things that make Bradley great.
1. Defense. Defense defense defense. And just to make it clear. Defense. Kid is the best on ball defender in the NBA bar none. It's actually a bit hysterical watching opposing guards bring the ball up the court against his full court press. Unless they are very athletic and have an elite handle, they will routinely struggle to get to midcourt, let alone score. Bradley is also a very underrated shot blocker, which is often not noticed because rarely do players even attempt anything besides fadaways against him. He's stuffed Wade, Johnson, and Westbrook (just off the top of my head) and all of those were multiple times. The things that make his defense great - his length, and instincts, will not regress. The only thing that could possibly regress is lateral quickness which won't happen for another 10 years or an injury.
2. Off the ball movement. He has a natural knack for getting open and moving off the ball. He's very Ray Allen like in his hustle and off the ball movement. If you turn his back to him for a moment, it's usually an uncontested layup or alley-oop dunk with Rondo. This will not regress unless he suddenly has a personality shift and gets lazy.
3. Explosiveness, burst, and ability to finish around the rim. While he isn't Derrick Rose, he's definitely near elite in all of those categories. The problem has always been he just doesn't have a great handle. Again, barring a sudden personality shift, and sudden laziness, none of those will regress. Shoulder has nothing to do with any of those as those are mostly legs and core.
Upside:
He's already a super elite defensive player with great athleticism. I'm not ready to say he's a knock down shooter as he was just stupid hot as a starter (shot 52% from 3 for 8 weeks IIRC), but he's definitely got great upside as a shooter. He also will be a great penetrator and offensive threat if he develops a better handle.
If he can keep his mid range shot consistent next season and keep knocking down corner 3s, along with improve his ball handling this offseason, he will be an elite SG.
Even if he tiers out and doesn't improve at all, he's already a very good starter. His defense alone guarantees he will always be at least a decent starter. I read somewhere that one game last year when Westbrook was guarded by him, Westbrook shot something like 2/15 and without him shot 4/8.