I find this idea very innovative and exciting. It is being developed by Fedilab, and separates data from relay (a bit like AtProto does) to allow everyone to keep their data, even on a phone

Holos - a mobile ActivityPub server that runs on your phone. A relay server maintains your stable identity when you're offline. Switch between text, photos, videos, and articles from a single account. Currently in private development, sharing progress with the community.

The account following the development has just 3 posts (with some light technical details) at the time of writing, but the stuff should be published on Codeberg soon.