Add "whisper comments"
Took a quick look and this hadn't been added to the issue tracker yet.
Whisper comments are comment that the submitting user determines should be posted within the thread in public, but which doesn't need full visibility. A whisper comment would be collapsed by default, perhaps only showing a small text preview of the first line in a small font.
The purpose of whisper comments would be for example to point out a minor error ("you got the year slightly wrong"), or spelling correction ("you mean definitely, not defiantly"), etc. Things that contribute, but doesn't need to draw attention away from the discussion.
Two possible ways to implement it:
Implement it via tags. When the user himself applies the whisper tag, it always becomes a whisper. Also, trusted users could tag something as a whisper.
A separate button in the submission form. To avoid abuse you then couldn't force another comment to be rendered as a whisper, perhaps only the most trusted users could flip that switch rather than anybody who can edit tags.