It's hard to tell really. Like many have already said, I think it depends on the team. If the young guys all pan out the way we expect them to and we build a contender, I don't think there's a limit to how good he can be. I think he'll win a few more Norris and maybe a Hart isn't out of the question if we go all the way.
IMO, a realistic expectation that should be reachable is PPG +/- 5 points. That's almost what he is right now but he's yet to reach PPG. 75-85 points could be his top end with an excellent defensive game.
But if you want to dream a bit, why not 90 points? No forwards even got 90 points this year but if absolutely everything goes right for him during a season maybe we could witness something truly magical.
As long as scoring is down like it is right now, I think that's the absolute top. 95-100 points is too high unless we get a year like 2005 where everyone is scoring like crazy.
Anyway, even if this year is his top end, we are so lucky to have him on the team. There's a very good chance he'll be the best player in franchise history (if he isn't already).