It's an interesting idea for sure, but I'm not sure how or if such a thing can exist. Moderation becomes a headache, and well, a lot of truly brilliant people I've met in life have zero interest in debating it. How do you keep out the YT commenters, Fox News or r/politics commenters, etc?
It would be interesting if HN had some bucket like /offtopic, for things that are flamebaity and removed from the main view, but I fear it would attract the aforementioned people who only ever troll there, and dang probably having zero interest in mod'ing it.
Have clear written criteria for what constitutes virtuous and unvirtuous conduct, and make it clear that commenters can be banned for the sort of angry, low-quality discourse that's the norm on those platforms. Then enforce it, with temporary bans at first and permabans for repeated or particularly egregious offenses. Most people won't want to be mods, but hopefully enough will.
I'm not speaking hypothetically here; I'm describing how moderation works on /r/TheMotte. I won't comment on any of the opinions expressed there since that's not the point: the point is that it can be done. It's existence proof that you can have a large discussion forum talking about controversial topics without it turning into an ideological monoculture or a cesspool.