It’d be every reply I think.

It’s partially fixable, by interacting with Mastodon the same way PeerTube does and have the community Announce only the posts. For everything else after that, it depends on whether the user is local or not. Anything a local user does could be sent directly, and if a remote user replied to a local user’s post, the local user could send a ‘post update’, for Mastodon to then retrieve the replies collection, circumventing the problem of us not having the remote user’s private keys. But if a remote user replied to a remote user’s post on a local community, they’d be nothing we could do about it (don’t have the keys for the ‘post update’, can’t Announce it without it being spammy either)