I hope this is the right place to discuss a potential feature for lemmy.
I've been reading a lot of the defederation calls from instances and their users. More often than not, this was due to very specific elements of those instances; trolls, extremists, etc... But in my opinion, defederating a whole instance because of that is a sad pity.
I was thinking a way to solve this would be to have a federated blacklist.
Instance Admins would ban user accounts from their instance and that would be added to a list that could be consulted/automatically used by other instance owners. They would ideally be able to set parameters, like banning users from a list accepted by a number of other instances, a specific reason for the ban, or banned by specific instances.
This would lessen the administrative load, protect instances, allow different instances with shared concerns to help each other while allowing their own users to interact with the 'compatible' users and communities from other instances.
Just an idea and wanted to bring it up and hear some thoughts.
Being part of an instance doesn't mean that it is exclusive to it at all if you can participate in it from any other instance. So I guess we just had a different understanding of what "exclusive" means?
As for the other question: You can just follow several similar communities on different instances right now, so if one instance gets de-federated or otherwise inaccessible you can just switch to another and so will most other people. Also, since your instance does cache remote communities, the posts in them do not disappear and are still accessible. Thus if a community decides to move they can post about that in the community and that notice will be retained on your instance for you to see later, even if the server the community was originally on disappears.