So VRChat showed us that we can force only verified 18+ players in Group Instances. How about you also add an option to force only poor and better avatar ranks in this or that instance. And it will basically lock your option to choose very poor avatars, like it does when your VRC+ sub is ended.
It will be even better if you will give the admins of group instances to "mark" zones where very poor is allowed in this or that world. Like making boundaries in Meta Quest. And who isn't in that zone, has their avatar not loaded.