Or better yet, a simple userscript. That way a single script could be run on all modern browsers with a couple of small tweaks required for the big 3, and easily installable out of the box on Opera and Safari.
Not a bad idea in the geekier circles, but the idea of installing something that supports userscripts and then installing userscripts isn't an obvious step for many users, whereas Google pushes Chrome apps and extensions quite heavily as an easy thing to play with.
Or personal scoring and coloured thread titles to suit. This isn't about the HN ranking mechanism, it's about finding and highlights article titles that might be interesting to the user.
In my case it really is about filtering, though, rather than discovery.
I like seeing things I wouldn't specifically choose to see, but I know if it has 'bitcoin', 'snowden' or 'CIA' in it, it's almost never going to appeal to me.
But yeah, if it was generic enough, such a thing could be used to highlight or hide, appealing to both approaches.
