If Alice makes a followers-only post, and Bob replies to it, to whom should Bob's reply be visible?
it's about principals
i chose "Alice's followers"
to me the imperative here is:
Alice "owns" their top level post and all replies to it
thus Alice's communication style overwhelms the style of anyone who responds to them, in that context
this has much further architecture implications than just your question. but for the matter here, all replies to a top level post defer on all communication style questions to style of the author of the top level post