I have a proposal to settle flamewars by the way. I had meant to propose something like this (a debate solver) for years. Here it is:
After 4 levels of back and forth (Joe says "...", Tim replies, then Joe replies once more, then Tim replies again), freeze that branch, hide it from the general public, and turn the branch into a settlement: both Tim and Joe are allowed one final comment each, that they both approve. Only once they have posted this compromise, is it shown in-place, where the original sub-thread used to be.
Simple. Prevents endless arguments. Good for everyone.
Hmm, I have had ideas for something similar, but which involves having to choose a side of the argument (ie, agree with parent or disagree) before posting. Once chosen, you can only vote on your 'side' (either up or down). Poor arguments on your 'side' can be killed with sufficient downvotes, so that the ensuing set of arguments hopefully ends up being the best set. This tends to happen in an informal way on HN, but only because people largely behave. In other forums, not so much. Perhaps glomming together your idea of maximum posts per user on a topic, along with side-based voting, some type of civil debating platform coudl be developed. After all, in actual debates you get 2 chances to state your position and a final sum-up.
After 4 levels of back and forth (Joe says "...", Tim replies, then Joe replies once more, then Tim replies again), freeze that branch, hide it from the general public, and turn the branch into a settlement: both Tim and Joe are allowed one final comment each, that they both approve. Only once they have posted this compromise, is it shown in-place, where the original sub-thread used to be.
Simple. Prevents endless arguments. Good for everyone.