@kissane The current set of Fediverse protocols *partially* solves migration.
Or to quote myself "This is definitely *better*, but is it good enough? Is it how it should be?" (rhetorical question, as migration is one of the major Fediverse selling points, the answer is "no")
https://jaxroam.vivaldi.net/2022/11/19/changes-of-address/
Far as I can tell there is no specification for user migration, what a conforming application and servers running it must do to enable this, and we need that.