So, it might be desirable to actually change ActivityPub. There are actually a lot of things I think ActivityPub really sucks at, but those could be fixed by extensions.
For Example, ActivityPod allows SSO style interactions which can allow Federated posts for comments in webpages.
This is relevant because technological decisions are typically made with respect to technological constraints and idealized users instead of idealized technology and user constraints.
The moment you put a person in front of a technological system, they interact with that system and change it, the system then changes the behavior and thought patterns of the user, which then changes the way they use the system.
Thus, these are cybernetic systems.
That's why dark patterns are leveraged. Without the cybernetic feedback loop the dark patterns don't work.
The problem with OSS, intentional communities, and open standards is that very often the cybernetic relationship is entirely ignored.
Attempting to reenforce norms through individual blame and social pressure, which is how these communities tend to deal with this, creates fragmentation in communities, and pushes people from those communities.
(I could write a whole other essay about how social cache is an often ignored source of power and is very frequently used for oppressive purposes, entirely enabled by group / mob dynamics.)
The solution is to create systems that structurally align with the values. In the case of Federation this could be only allowing federation with communities that implement certain protocols, and amongst those protocols could be Kripke Relational Semantics defining who is and isn't allowed to repost a toot.