What I’d much rather see is instance based accounts, however, with the ability to take over/migrate them from other instances, so that if an instance goes down, people can still keep their identity. It would also allow instances focused on protecting minority communities to keep doing that.
This exists right now. It has existed for longer than Mastodon, much less Lemmy.
Established by Mike Macgirvin in 2011 when he invented nomadic identity. First implemented in his Zot protocol from 2012 and a Friendica fork named Red, later Red Matrix, known as Hubzilla since 2015. Also available on (streams).
Not just a vague concept or an experiment, but daily-driven on stable servers since over a decade.
Nomadic identity goes even further than migration. Nomadic identity allows you to have the same Fediverse identity with everything in it (name, posts, connections, settings, files etc. etc. pp.) on multiple servers simultaneously. Not dumb copies. Bidirectional, near-real-time, live, hot backups. Whatever happens on one instance of a channel will be sync'd to all others almost immediately.
One of the clones goes down, doesn't matter. The main instance goes down, doesn't matter, you can use the clones just the same. The main instances goes down and stays down, doesn't matter, you make one of the clones your new main instance. All your nomadic connections are automagically changed to your new identity based on your new main instance. Yes, even on remote servers.
Even migration is based on the same concept. If you move from one server to another, first a clone is created, then the clone is declared the new main instance, thus demoting the original instance to clone, then the old original instance is deleted and the account with it. Not only can you move with absolutely literally everything, but you don't leave any rubbish behind on the old instance.
Only downside: It does not work on ActivityPub. Yet. It requires a special protocol, either Zot (Hubzilla) or Nomad ((streams)). ActivityPub-based projects don't even understand nomadic identity. So when you move, you have to reconnect all your non-nomadic followers.
ActivityPub implementation is being worked on, at least in theory. But the guy behind all this has, well, apparently not fully quit, but dramatically slowed down.