That's an excellent analysis, thank you. One thing I wanted to expand upon: > posts/root-comments with engaging comments subthreads would still rise to the top

That's an excellent analysis, thank you. One thing I wanted to expand upon: > posts/root-comments with engaging comments subthreads would still rise to the top, to ensure that those subthreads are surfaced to appreciate. (Probably there'd have to be UX for this case, highlighting the aspect of the post+comments that's so engaging.) I think HN does something like that, and I appreciate they don't have any particular UX to indicate any "surfacing", but it's just organically applied to the ranking. Example: * Just posted top-level comments get the first spot for some time, so people have a chance to interact with them. Often you open a big thread with hundreds of comments and the first comment is 1 minute old. That's great. * I'm pretty sure HN (and possibly Reddit, but I have no evidence for either) rank a top-level comment higher if a reply has a lot of votes/engagement. * I'm somewhat positive HN downranks top-level comments that have a very high number of downvoted/controversial/high comment-to-vote ratio replies. I'm certain HN does that for posts (comments > vote = probably controversial post, slightly downranked). * All of these things don't require UX, so they're a little opaque so people won't try to gamify their comments to manually nudge them toward some position in the thread.