If I understand correctly he’s talking about the ability to export your account data and then import it to another compatible fedi server. Other software (mastodon, latest version of lemmy, etc) also do it on a client side, so I don’t think any changes to AP will be necessary.
What is concerning is his wording about “to leave threads”. Consider that whatever saying in this interview is carefully laid out beforehand. What reason is there for a corporation that is living of it’s users to just so casually let them leave like they please with everything that is giving value to Meta? He is not talking about wanting the users to leave threads, but to be able to migrate either direction. Who is going to win that fight in the end? The corporation who’s solely goal is to win or the free and open community that is so tolerant that it invites the beast it fled from?