I agree that Brilliant’s threading is an imperfect implementation; however, I think it’s interesting because I think the worst problems with their UI are just exaggerated versions of inherent problems with threading.
Take my remark that threads are meant to be read exactly once and not to conduct a month-long discussion. For some background, the top-voted comment is by me, about a github repo I started relevant to the subject of the thread. The thread itself was also about a competition which I participated in. As a result I had a particular interest in at least scanning all new replies. Have you ever tried reading a threaded discussion and then coming back to it? (reading only direct replies to you does not count) It’s awful. You basically have to look at every single post to find the new ones. It’s actually impossible to come up with something worse. I guess you could maybe argue for a software that auto-collapses all threads that contain no new replies so you can just read the expanded threads on new visits, but I’ve never seen a forum that does that because the very sites that would see the need for such a feature aren’t using threaded discussion at all. Another alternative is just including an email subscription system that includes the text of new comments with the email, but this is essentially admitting the UI is broken by allowing me to not use it.