Can you cite the sources that say there is a significant bump after year 3 or did you just pull that out of your hat? Because I've also heard the biggest jump is between years 1 and 2. And guys like Deron and CP3 (and many others) made a huge leap midway through their first seasons. You are right, players develop at different rates. However, based on the fact Trey has shown very little improvement, and maybe even regression in terms of selfishness, many of us don't believe a huge light is going to go on this season. But who knows, maybe it will take Trey four years or six years before he turns into this magically wonderful PG.
I feel like it's pretty common knowledge, Stifle, that historically point guards see the biggest jump between year 2 and year 3. I recall reading it in a Nate Silver piece (or maybe his book) fairly recently, and I also remember that everyone was astounded at the improvement that D-Will showed between year one and year two, since that was historically irregular. I'll see if I can drag up some links when I'm home.