It’s never been possible to change the full diaspora* ID (username@podname.tld) – mainly, I think, for reasons of federation breakage.
However, once the account migration feature has been implemented, this should no longer be a problem. If it’s possible to change a diaspora ID to one on a different pod – and, I assume, the username doesn’t have to be the same on the new pod as on the old when migrating – it should technically be possible to change the username while staying on the same pod without breaking federation.
In the worst case, this would be a kind of ‘within-pod’ migration, although hopefully there will be a solution that is simpler and costs less in resources.
Those are my thoughts and hopes as someone who really doesn’t understand the technical side of things – now, technical people, shoot me down!
This already kind of technically possible since 0.7.0.0 using the account migration feature part, which has been merged.
A podmin can do that by creating a new user profile (User model) and then creating a account migration record (AccountMigration model) with old user set to old user profile and new user set to new user profile. After that you the podmin runs the perform! method of this account migration object and the thing is done.
One limitation I can think of, is that the podmin can’t create a new user with the same email as an existing one. But the email of the new user can be set to the same value after the migration is performed.
I don’t think we tested this intensively, partly because not too many people aware that it is possible. But if there is a user who wants to change their diaspora* ID and a podmin who is ready to perform the required commands, it is totally possible.
And if your proposal was to make this an official feature with its own UI, then I think we should test it first as a “podmin driven” feature and when we’re sure it is stable enough we can implement some UI for this.
There is no “simple migration” possible, changing the diaspora ID is normal migrations with all limitations of a migration (the target username must be free and a one way migration, it can’t be undone). But as senya already said, it’s possible, there is just no UI for it yet.