There is a partially finished beta here
and the author invites someone to finish it off. It is a very good idea!
Some boards have awful problems with unrestrained ‘swamping.’ I know of one board where a single member chalked up 27,000 posts over several years. Other members get discouraged from posting when they see theirs drowned in a welter of replies from a few members who dominate the board.
Incidentally, I think a mod like this would need to differentiate between new topics and replies. For example a member (or group) may be allowed 10 replies per day but only one new topic per day.