Thanks for the links. But I'm one of those who try to avoid extensions unless absolute necessary. I can't have all these extensions on my mobile devices too. It's possible to write a tiny bookmarklet that just looks for the spacers used to indent the comments. However, this is something very basic from usability point of view hence I'm making a suggestion.

It's going to come eventually. In fact, it may be the only major change to the Hacker News UI that we're committed to. But we don't yet know when.