@evan it nonetheless sounds right to me when the conversation is initiated as followers-only; a choice for a semi-private audience. Each conversation thread should narrow in to smaller audience, even if that means eventually parts of it are essentially mention-only.

@novelgazer the original post and the replies don't have to be isomorphic. If I post a photo of a bus, do all the comments have to be photos of buses? No, obviously not. A "followers-only" conversation where every post is visible to each author's followers is meaningless; it's much more important and natural to have a conversation amongst a group of people.