One of my sites has a long-standing comment problem. When a CM collected stats for us in 2014, 2.1% of our posts had more than 50 comments. That's absurd, and the problem has continued. Moderators spend way too much time dealing with comments and flags on comments and complaints on meta about deleted comments and sniping about comments in other comments... for a second-class feature, comments sure do cause a lot of work. We haven't been able to bring about a cultural change yet; can we add some friction?
The answer isn't to prevent comments because, while some people love to use comments for tangents, arguments, jokes, and long-winded discussions, comments do still serve a purpose. We also get the good kind, the ones that seek clarification or otherwise try to improve a post. And that's why we don't just purge threads wholesale; we need to preserve those ones if they're not yet obsolete. We want the good comments; we just want fewer of the others.
Instead of cleaning up the problems afterward, it would be great if we had some way to impede some of those comment explosions in the first place, on sites where this is a problem. How can we do that? I can think of a few possibilities:
Lower the number of comments needed before you get the "let's continue this in chat" suggestion. This currently happens if two users have posted three comments each, so there's not a lot of room to improve this. I see two downsides: (a) people can ignore that prompt (unless we change that), and (b) this does nothing for threads involving several people.
Have something like protection that restricts commenting. This would allow moderators (or the community, preferably) to prevent drive-by comments on posts that are getting a lot of activity. Like protection, it should require a certain amount of reputation on this site to be able to comment. This helps with Hot Network Questions but might not make much of a dent otherwise.
When comment rate reaches a certain threshold (N comments/hour), temporarily prevent further comments (for some number of hours) -- maybe from everybody, or maybe just from people who've commented more than M times already. The idea of rate-sensitive commenting limits is attractive, but I'm unsure about how it should work.
Would any of these work? What else could be done to address this problem? (I now see that I made a couple more quasi-suggestions elsewhere a while back.)
This question arises from one site, but I've seen comment explosions that could benefit from some throttling on other sites too, so it's not only one site's problem. I'm looking for something that sites could opt into, not something that would be mandatory across all of SE.