The biggest is accuracy on the gimmies, but you know that. Don't have enough data this year to really say if he improved on that or not.
Every QB in the NFL is always trying to improve his awareness and reads, no matter who you are. Teams try to throw new things at you to confuse. Caleb is no different that he can improve in that department. If you watched closely last week he went through his progression, when he could, and had to check down cause no one was open for whatever reason. But that seems to be left out.
With a QB like Williams, OC/HC walk a fine line in reining him in but also letting him do the things he does that are special. He made a garbage throw/decision on the pick, it happens. The thing is, that doesn't happen all that often. Sometimes you have to live with a little of the bad to get the things only a few can do in NFL.