Reading this thread back, it would be very cool if gang agression would be related to a few aspects:
- Player's clothes: Neutral clothes would be mostly ignored, clothes with the color of a rival gang would be met with agression towards the player, fancy clothes would attract muggers.
- Player's car: A common or lower-end car would be mostly neutral, fancy cars would attract more carjackers, police or gang cars would be negative.
- Player's actions: If player is just walking around it would be neutral, player acting like an idiot pointing a gun and stuff would be negative.
- Story: If any missions involved the player attacking said gang, they'd generally act more agressively, could be avoided by wearing a mask in the mission.
This way you had a chance of exploring gang areas without being shot to pieces in seconds.
As for carjackings, maybe a similar system to San Andreas', where a ped would just randomly drag you out of the car. Would also be interesting if you had a random chance to recover your car, either abandoned on a back alley somewhere or at a police station.
As for muggers, GTA IV had a system where you could give money to sax players and hobos, so maybe a system using that would be cool: one or more NPCs would point guns at you, so you had to either press a button to give them $100 or try to fight back.
This is a great idea, would be good also if every part of the map you were in had different dangers for example in known ghettos you need to be careful of local gangs but with less police presence because police won't go in really dangerous hoods.
Also as you progress through the game your actions could lead to more heat with certain gangs or the authorities forcing you to become more tactical with where you go and what you do there.