Perhaps add the ability for a poster to retract his orher pending comments? You could add a mandatory waiting period to prevent abuse.
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.
Edit: After some observation, it appears to be two hours. I don't want to be pissy about this, but this is what I was worried about in my other comment--you seem to be making this drastic change with no little thought to how it will interact with the systems and behaviors already in place.