Yes, I think I misunderstood your previous comment, and thought you were proposing a universal mechanism for the definition of business logic. I agree that every vocabulary should be accompanied by a well-documented text that describes all the linked data formats, message exchanges, and the conditions on which they take place.
With the FEP’s we are moving in that direction. Docs may be spiced up with ActivityPub sequence diagrams such as @boyter started to create. And FEDERATION.md convention may be improved to have an easy way to find what an app support. I still think Compliance Profiles come in handy as a way to discover the functionality that is available.