ActivityPub is a product of Architecture Astronauts. Start with a simple idea but generalize it too far, so it can do everything, so much so that no one understands how to do the simple stuff. You have to understand the theory before you do can anything pragmatic. It's why I said last week that they need a BDG asap, with implementations in all major runtime environments. I would help them design it, I'm a fairly typical "busy developer." I would support it if it were easier to understand, thus more likely not to be revised with breakage to apps. I've also seen this happen before, in fact it happens more often than not. If you don't understand a format, you can't actually support it. This is part of the you can't lie to a compiler axiom.