There is already the activitypub client to server protocol but there is 0 interest in it.
https://codeberg.org/openEngiadina/cpub (though parent project switched to XMPP)
https://github.com/andstatus/andstatus/issues/499 (though stalled)
Neither am I convinced whether activitypub takes itself seriously as they don't keep a validator up. Nor is there a reference implementation, is there?