1. Organic city change
Following on from the enhanced NPCs, the city needs to be able to change by itself. If that guy who you ran over and killed died, then his family might struggle for money, meaning they have to leave their house. The road had already become quite empty a few weeks prior after a few families moved out, so teenagers take it upon themselves to cause some damage to the buildings and add some graffiti. After a few short weeks the road changes completely and is almost derelict, with most the street being empty and barely a car going down it. In someone else's game a property developer might come in and demolish a large area of land and build a supermarket. We know it's pretty far-fetched, but it would be incredible.
2014 is a long way away, but what do you want to see in the next generation of the GTA franchise on the PS4 and Xbox 360 successor?