@occultist8128@infosec.pub "followers only" is a concept that is Mastodon specific, and Pixelfed supports it.

There's nothing to change at the protocol level itself.

Sending the reply to OP in your example would be a betrayal of the visibility of followers only... which is kind of silly but technically correct.

Better would be followers + participants, but that's up to the individual implementors to adopt.