See...these are the kinds of things where if Justin never does that, never even sniffs that, nobody should be disappointed in the least. Without meaning too you have inadvertently annointed him as a Top 10 center and All Star candidate after a couple of good energy games in the season's garbagetime.
Teams will adapt and adjust once they realize they have to -- not til next year most likely. It will get harder. I have been lobbying for Justin to make this roster and get a shot since last summer, when I was amazed to see that our front office could not distinguish between a nice little hustling tweener in Admundsen and a potential lane clogger in Williams. But if he ever gets to the point where he's a dependable rotation 4/5 it will be a great day. I agree with you with the sorts of things he would need to add to take the next step -- a little half hook, maybe a standstill jumper out to 15' etc. -- but those are the very skills that are difficult to master and which separate the best bigs in the world from the rest. If they were easy to develop, everybody would already have them. Most guys can never master them at all, at least not at an NBA level.