From time to time, when we get either the "too many comments" autoflag or someone raises a flag to tell us that there are a lot of comments on a post it would be useful to be able to add a comment or notice along the lines of:
This post is generating too many comments. If there is anything worth saving please post it as an answer or an edit to the post. All the comments will be deleted in due course.
This is not the same as the "move comments to chat" option. This is for the times when the discussion people are having ends up answering the question in comments.
It needs to be pinned so that people see it and have a chance to act on it before the comments are deleted.