One thing that definitely worries me with federation in general is the barrier to entry to hosting an instance is low, by design. On one hand this is great, but on the other hand it means just about anyone can spin up an instance and collect usernames, passwords, emails, etc. from anyone who signs up
I know this is obviously no better than an single giant corporation who can do that. But it's interesting to think about.
I'm definitely not suggesting kbin.social is doing this by the way. Your post just spurred this thought for me
Regardless of the current situation, I think the option in general to "unsubscribe" from an entire instance could be useful. I know we can create our own instances and defederate, but not everyone has the skills, money, etc. to be able to do that.