In era, not all gangs are basing gangs, and era staff focus on them mainly, heres some cool ideas though:
1.classification: gangs can classify other gangs as rivals, this would show rival gang members on the map with a red outline, and also have the red outline on the avatar itself.
2.rat filter: every time a rival gang tries to send a rat in your gang, it will send you a notification saying that this person is or was in a rival gang.
3."hits": you can mark an enemy in a rival gang, and send members out to kill that enemy. Only the highest ranks can assign hits, and they use their own cash.
4:enemy look & prizes: killing a rival will give you things like a small amount of cash, and some ammunition.
5.gang types: you can have the ability to classify your gang as "mafia, military, police, or social"
6.jobs: gangs can play jobs to give them more money (like on zone)