Comment by JeremyNT

In which case, a "time out" is redundant if the goal is to simply avoid locking users out.

This system seems to skew discussion toward already popular / active topics, though, since there is less risk of being stuck pending there. Perhaps allowing for multiple pending comments per user (with a limit based on karma, or length of time on the site) would make it less "risky" to post comments in unpopular discussions.