@scott I don't think so. Other Hubzilla or Friendica instances that receive a Hubzilla post over AP can still boost it over there, right?
The reply control from your instance won't stop Mastodon users from replying either (though it will stop you seeing those replies, and to some extent will reduce the visibility of replies).
I think it all comes down to what's outlined in https://foggyminds.com/display/c6ef095f-1165-ce77-d6de-73f618365846 (saw that post a little after my reply above) and open federated social media in general being built around own-access-choices rather than data control, outside of posting modes with very limited reach which *should* be implemented with more privacy than they are.