This makes me wonder: isn't this basically the perfect thing to bootstrap a decentralized DNS with? In a messaging system there's no reason you'd ever want to revoke control of a domain, and the idea of genuinely-anonymizable communication should be appealing to just about anyone.
I might not be thinking broadly enough here though.
I think decentralized DNS with machine readable addresses is basically a solved problem (e.g. Magnet links or Tor Hidden Services).
A domain in this case is akin to a hash of a public key, or something like that, just enough to securely identify the target of the communication so there’s nothing to “revoke” although that’s not to say the peer discovery systems could not try to blacklist you.
Decentralized DNS with human readable addresses (unique screen names) is perhaps more a political problem than a technical one, and hence never fully “solved” just different sets of trade-offs that can be made.
Social attestations are another solution to this, unless you count them as an authority over issued names. “If all my friends are convinced this person is called Bob, that’s good enough for me”. Doesn’t help with uniqueness though, but that’s what we have keys for.
I'm not talking about the technical problem, the technical problem is solved (including for human-readable addresses, which is the part that actually matters), I'm talking about the political part of the problem. "No one bothers with decentralized DNS," here's the problem space it's the killer tool for.
Worst possible case you can drop the messages from a domain, which is how federated systems already work.
There's no reason to ever revoke control for messaging systems, though, genuinely: imagine if your e-mail address could be taken on a whim by anyone. It can be! But you'd never want to revoke control of a domain rather than just marking it as spam or illegal and dropping messages from it. It functions as an inbox more than it functions as an outbox.
I might not be thinking broadly enough here though.