Yes, that may be on the short term for interoperability when federating. ActivityPub spec does not prescribe auth/authz methods but suggests to use either HTTP Signatures or Linked Data Signatures (see here). I don’t know if any fediverse apps support LDS at the moment, but HTTP signatures were mostly chosen for practical reasons (like also WebFinger for Mentions).
That is why Solid joining the SocialCG is so potentially interesting, as there is spec-level talk about the future of AP/fediverse, and maybe further diversification can be avoided.
This is what I’m most interested in. In openEngiadina @pukkamustard is investigating a bunch of ways to integrate Linked Data with AP. Ideally many, many vocabularies should be able to be adopted in various contexts. In AP it suggested to just ignore any message properties that are not understood.
Mechanisms for the support of all these vocabularies (e.g. modularity) and also any domain-specific extensions to AP message formats themselves are still to be further elaborated for the most part, AFAIK.