They would be a great place to setup a workshop or caravan but would cost a lot more more to setup, they would be non agressive and never start wars, but they would have massive garrisons of verry powerful merc units so they'd be hard to capture. They would be home to unique mercenary companies similar to the current minor factions and the player can buy a barracks in a city state to start their own mercenary company wit the barracks acting as a garrison for your troops. You can hire a recruiter and tell them what units you want them to recruit and based on their leadership skill you will get more and higher level units.