Often one big problem is that users feel attacked and answer in a topic whereas a private massage would have been enough.
If there was a flag option to move a message into a private conversation this would preserve that only posts staff public that are of a lot of public interest.
There even could be a heuristic, that tries to detect such posts. And a button for the author at the latest post to convert into pm directly.
Especially for new users such a button would be a big benefit for the forum
I think many topics end up being a chat between just two users that could have been solved outside the topic.
On the goal, to get clean, valuable interesting topics, It would be a good advise to “chat” in private messages and only post in the topic if you have to say something of global interest
Excuse the bump, but I was searching something else and this topic popped up. Earlier today I saw a thread on another forum that would have benefited from this feature. A thread had got rather personal, with just a handful of posters discussing sensitive issues. At the request of the participants, the moderators deleted the thread and the posters continued the conversation in PM.
What would have been good (and should be easy, given the common underlying framework) is to convert the Topic into a Conversation, with all posters on that Topic as participants.
I think of it as a “get a room you guys” button.
That would be great, to mark a whole topic as “private visible only to participants”
If a topic got “spammed” with such a private conversation, those posts could easily be moved into a new thread and that new thread could be marked private then 
You have selected 20 posts
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Between @watchmanmonitor and others, this has been requested enough to be on my radar…
This request about redirecting incoming posts which were held for approval is related.
