Yeah that part we can probably discuss in a [future] separate thread, unlikely to help silverpill draft his FEP, and could lead to long sidequests about legal liabilities and compliance 
FWIW the Threadiverse group has been working in overdrive on this all summer, and my governance intuition is that anything this general and critical to cross-form-factor/user-story interop should ideally be hashed out beyond the microblogosphere at the “protocol-wide concern for corner-cases” level, not in “my users and their UX are my only concern” mode. Here are the FEPs I know of that might be relevant:
- FEP-400e: Publicly-appendable ActivityPub collections
- FEP-db0e: Authentication mechanism for non-public groups: “mostly intended to supplement FEP-400e.”
- FEP-1b12: Group federation
- exhaustive socialhub thread “reconciling” and interoperating between the two above
- by way of comparison, it seems bsky’s ATProtocol has no group actors or plans to have them in-protocol?! i wonder how feeds like blacksky are built, given this constrain.
(a, silverpill, and probably steve are well aware of this, but just for posterity and people who randomly find themselves here, thought cross-links would be helpful to catch people up)