That’s a really solid rule for productive discussions. The great difficulty would lie in actually enforcing it on HN.
Maybe some sort of cool-down timer for posters, who are otherwise polite, getting too agitated? Some kind of rate limiting for new comments on a controversial submission?
Hacker News actually already has that to a first approximation (though if I understand correctly, rather than being applied to heated or controversial threads, it's applied to users who have difficulty consistently adhering to the site guidelines. Their accounts are flagged as not allowing more than a certain number of posts per hour).
Much better: bots insert fake responses that are calming and neutral. If you want to tailor/manage discussions (manipulate might be a better word), it seems like adding to the discussion is far better than censorship (or rate limiting as you call it). People being shadowbaned or rate limited or whatever just aggravates the problem because it makes people more hostile in general. Don’t censor bad speech, promote what you believe to be better speech.
Maybe some sort of cool-down timer for posters, who are otherwise polite, getting too agitated? Some kind of rate limiting for new comments on a controversial submission?