On one level it could be a simple bookmarket (bookmark with JS). When clicked, it goes through the HN discussion page. When it finds a top HNer's username, it (1) colors it and (2) shows the category if that HNer is in the top or bottom 10% in any category.

For instance: edw519 33 minutes ago | link Top: Cheerfulness, Orderliness, Gregariousness, Agreeableness Bottom: Imagination, Authority-challenging, Intellect

(I'd also something that shows me when a commenter is somebody important, even if not a karma king.)

Ok this actually makes a lot of sense. When someone replies to you on Facebook, you generally know who they are. On Hacker News, you have no idea. Including some basic (albeit imperfect) information along with a notification reply could be really useful.

This could even be true for the follow-feed mechanism. If you're following someone on Twitter or friends with them on Facebook and they write something that appears in your feed, you are already familiar with the author on some level. In the Hackbook extension, it's fairly common to follow people and not know much about them at all. Again, including some basic Watson-generated information along with the "a user you're following wrote a comment" newsfeed item could be helpful.

Let me give it some more thought and maybe I'll have time to work on it this week.