I think there is some balancing that can be done to prevent bad faith twitter users from claiming space in the larger instances. The day twitter goes down, maybe capping the number of new accounts created daily could be used to prevent ban avoidances and agitate them off the fediverse or into smaller instances.

Also, I think the current model of a fediverse will definitely have cesspools regardless of where the users came from. We do have loli and pedo instances unfortunately.