Well, #1 is kind of impossible now. Different people can have the same ID on different instances.
#2, unless they really want to just be their own separate community completely, like an entirely different website, then yeah of course. That’s the point. Regarding the current major defederation, my understanding is that this not meant to be permanent and is a different situation. It’s a workaround basically.
There is now though. So why not federate again?