This is actually something that I've been thinking about Lemmy too. Now Lemmy.World is a good instance, but if I ever need to move, I'll lose a lot, and that's not what Lemmy and the Fediverse as a whole should stand for. We need to allow users to migrate to another instance as a whole. Not just the name, but the messages, posts, replies, everything should be repointed to the new user.

Of course, this brings new and interesting attack vectors on instances for DSoS and for users data. Identity theft would be a real bitch.