@smallcircles @steve I think having machine-readable specs is possible, but it's a lot of work. I think human-readable documentation is a better starting point.
I've got a goal to add FEPs for Event management, geo-social, and relationships. All covered by the Activity Vocabulary but not ActivityPub. I'd be happy to extend the FEP template with specifics for activity types, expected responses, and object types and try these application areas out.