As far as more client rulers than family members, while that's sure to happen just based on the fact that you're going to have a lot more cities than family members at some point, I don't think it hinders things too much since the members you do have will be having children, and they'll be having children.

Now I can't speak for late-game balance, as I'm only 20 years into a campaign myself, but I expect things to be all right.