I like these ideas, at least as an experiment … sounds like plugin territory to me to explore the value of such a technique.
I guess the key to how effective this would be would having a hard working, fair moderator that was themselves patient and able to work through the discussion in detail to pick the right people to take it forward.
The only issue I see is sometimes you get that special contribution from some random that resolves the argument somehow by bringing some new perspective or a calming, rational presence. If you are actively shutting others out you will lose those sometimes crucial contributions.