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 shuta 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.