This is very cool research. I would love to see topics like this built into a browser extension (or even into HN itself although that may be beyond the scope of HN's core features). I find that there's a decent bit of content that gets posted on HN that I'm not personally interested in and, on the flip side, there are times when I want to go more in-depth on a topic but can't find more posts that cover it. I don't really want a whole subreddit-style navigation system, so some automatic topic tagging could be a nice middle ground.