[account42]

As much as I like threaded discussion like on HN I think it makes following discussion over a longer period of time almost impossible as you need to look all over the tree for new replies. Even reddit's highlighting of new posts does not really fix that and is s paid feaure anyway (except in the subs you moderate) so won't have any effect on the nature of the community. Maybe having both a threaded view for the first time you want to read through a thread and a more linear view for updates would make sense.

[Alex3917]

Scoop places a [new] tag next to comments that have been posted since the last time you refreshed the page, so that you can just Ctrl-F. So there have been popular sites doing this for 20+ years, e.g. Kuro5hin and DailyKos. HN just hasn't had features like this due to being limited by single threaded compute for various reasons. Although if the comments were served via an API, this could now be down in the front end with just the timestamp of when each user last refreshed each page.