Way back in the demo video, we saw the option to fight a gang, take his ****, and plant a companion there. Is this still being worked on? I can't seem to pick fights with gang leaders, only work for them.
You can pick fights with the gang leaders - you just need to go into the town scene and approach one of the back alleys/waterways/etc that they control. Pick a fight with the criminals there, and when you defeat them, you get the option for staying around and fighting the leader. It'll be a fight of your party (in their social outfits) vs some custom thief troops and the gang leader. If you defeat them, you get some trade goods + normal fight drops, relation gains with the owner of the city and the other gangs of the city, and a relationship drop with the gang that controlled the territory. That gang also loses control of the territory, (seemingly?) lowering their noteable's power. As far as I know, you can't take over the territory - but it's not a bad way to get some XP and relations, plus control who has power in the city.