I cant really think of any hop ups that would make the car any better..well I have not seen any that screams buy me NOW!..
I think in a short while we will start seeing a few parts that will address a few of the problems that the Pro 4 has,The front one way gears(in defense of the Pro4 I hit something really hard,I think it would have broken any car)and from what I have read the chassis gets tweaked easy(I have not had this problem)So I would look for a 3mm chassis to be out in no time.