@evan I'm not sure which aspect you're referring to. I don't see any separation as long as the there's linkage between broadcast post and non-broadcast post (e.g. I could reply to this with "direct" visibility, and then you could respond with "public" visibility, effectively breaking the entire conversation thread in public 馃ぃ).
Renaming "direct message/mention" to "private mention" by Mastodon feels like a solid first step in the right direction.