These are the things that I am hoping will be in Grand Theft Auto V:
Car modification garages.
Being able to buy safe houses.
Being able to ride bikes again.
Dual wielding of weapons.
The shadows looking better than they did in GTA IV. (console version)
If people can call you like in GTA IV, there should be an option to only receive story progressing calls.
If the phone can take pictures like in GTA IV, you should be able to save the pictures you take.
Being able to dive while swimming.
Having a radio station that you can choose which songs on the hard drive will be played on that radio station (console version)
Having a first person camera when driving. Not that "camera on the hood" crap like in GTA IV. You should be able to see inside of the car.