Make it trivial for users to move their accounts between instances, and very hard for instance admins to block. Ideally it would be possible to migrate an account even after an instance shut down, but that is probably impractical to implement.
We also need to consider how to mitigate the threat to communities (I think that's the term. Lemmy's equivalent of subreddits). If big communities are tied to specific servers then we have the same issue with server admin power.
Building on this, screw designs have evolved with technology.
Pozidrive looks like Phillips, but was designed so that the driver slips out without damaging the head if too much torque is applied. It was useful for early car assembly robots, which couldn't control the amount of torque they applied. They'd just apply as much torque as possible and the head would slip at the right point.
As the technology improved, it became possible to control the torque the robot applied. That lead to Torx head screws. They're designed to maximise the torque that can be applied without slipping. In modern car assembly, the robot tightens the screw to the designed torque automatically.