What I am thinking as a possible solution would be to have some type of "community server", akin to email list servers. The admin of the server becomes a "mere" service provider, and those that create communities are then responsible for moderation and that content being hosted there.
I believe that this would be perfectly possible to implement with Lemmy, so much so that I will add some of this functionality to Fediverser as part of my NLNet grant. The question is: who else would be interested in hosting these fediverser-enabled instances?
Theoretically, any admin would still have access to the server and make changes to things.
Practically, no. Anyone providing this service would be a hosting provider. If something bad happens at the community, they would only be able to claim it's not their responsibility if they are able to point to the actual moderator who is liable.