This is an absolutely bare-bones feature for HN. It would make the site so much more usable in general. The big case for collapsible comments relative to HN is stories where the top voted comment is only semi-related to the article (usual suspects being security, software freedom, political leaning freedom, ...) but spawns its own megathread and drowns out any hope of other discussions more germane to the original post.

Even if the don't collapse, It might be nice to see first level comments have some kind of distinguishing visual context...to get to another thought... eg, comment number 2,3 etc...is ofetn buried under 1.1.1.1.1.1.1.4 sub comment discusion minutia....when a top comment has 30 or 40 sub comments.

you should be able to scroll a page and pick out the top 5 original comments...even without collapsing...

Official word is that it'll be the "only major change to the Hacker News UI that we're committed to"

https://news.ycombinator.com/item?id=8297695

This seems to be the most obvious thing they're missing. I can't stand trying to read through HN comments without a greasemonkey script.

One of the problems of collapsible threads is that it reduces the amount of people who are prepared to flag and downvote comments that shouldn't be here.