A lot of this doesn't work easily on the activitypub model, because accounts and posts and communities live on their host instances, and every interaction has to be relayed to them and updates have to be retrieved from them.
While you can set up mirrors with arbitrary additional moderation that can be seen from everywhere, you can't support submission of content from instances blocked by the host instance.
The bluesky model with content addressing can create that experience by allowing the creation of "roaming" communities where posts and comments can be collected by multiple hosts who each can apply their own filtering. Since posts are signed and comment trees use hashes of the parent you can't manipulate others' posts undetected.
Bluesky already has 3rd party moderation label services and 3rd party feed generators for its Twitter-like service, and a fork replicating a forum model could have 3rd party forum views and 3rd party moderation applied similarly.
Without content addressing that's almost impossible