Interesting point. With activitypub, Threads could try to avoid enshittification.
The Problem: Threads, Mastodon and the other Fediverse apps will soon not be the only players in the Fediverse. At least letting die Facebook of enshittification will not work at this point. And additionally, if Threads decides to franchise its own instances, you have tiny thread-instances all over Social Media not even operated by Meta and that seems pretty resistant to enshittification.