My Wishlist for the next GTA Game would be as following:
Something like the Big Bang Cheat from Vice City.
The Hydra Jetpack like in San Andreas.
A more modern looking Rhino Tank.
Some Firework Rockets.
Ability to go in every Building you want to go in.
Some BMX Bikes like in San Andreas.
A Skatepark like in San Andreas.
More Airplanes and Helicopters.
A Theme Park with Rollercoasters and other Rides that are not closed down like in GTA IV.
Some cool Car Cheats!