staion I'm still having some difficulty wrapping my head around your distinction between Private Messaging and Private Discussion. Can you elaborate or clarify a bit more? Thanks.
My understanding is as follows:
Private Messages
Personally, I see what is being developed here as a Private Messaging feature. It is allowing me to select specific recipients (as I would do so in other messaging services or in email) and post a message, beginning a conversation with only them.
Private Discussions
I currently run a Flarum instance for a small team and have configured certain tags and permissions so that a number of different private discussion spaces exist on the forum. Only users with specific roles are granted access to those private discussions.