I've played onn servers where illegal roleplay wasn't dead and gangs were thriving, and I'm not sure if your idea will not work out.
Well established gangs should not have to worry about new, poorly developed gangs popping out of the wood work and start claiming turf, let alone the same street.
I've seen it myself, It'll lead up to forum reports and poor reasoning to deathmatch.
People who are looking to create a new faction within or close to a well grounded street gang, try to establish them besides the already claimed turf, one or two streets over. It'll create a realistic conflict between the two factions over the street they're looking to claim. Aslong as it remains realistic.
I understand you on that one. People tend to claim a lot of turf even though they don't have the members to back it up with. A place such as Bohan is pretty big and could fit a lot of street gangs. Street gangs should control nothing more than a few streets or a project complex. I doubt there will be a street gang that controls one whole side of one borough.