Since it's mention-undocumented-endpoints day, https://news.ycombinator.com/latest?id=$ID does that, where $ID can either be a story (in which case you get the entire thread sorted reverse-chronologically) or a comment (in which case you get the comments in that subthread).

So, for the current thread: https://news.ycombinator.com/latest?id=41228935

or for a subthread: https://news.ycombinator.com/latest?id=41229914.