What made everybody move from a corporate social media platform to another corporate social media platform instead of the fediverse?
After all, the Fediverse and Activitypub is much more mature than Bluesky and the copycat AT protocol or Threads and … whatever they use.
Not leagaly but users will be frustated and leave. They will rollback within a day so you will not need to worry too much.
“users will be frustated and leave” exactly the same thing can happen to an instance that adds an instance (or wildcard domain) block. I’d be very surprised if no instance has ever rolled back a block.
Users don’t need to worry about instance blocks on ActivityPub, any more than they have to worry about DNS RBLs for email.