Prioritizing feeds is something I have wanted too, and it appears to be coming in this newsreader that emulates a mail interface--but what I really want to do is be able to subscribe to comment pages.

I coded a new site that's not quite ready yet, though a few people are using it. It not only offers feeds for top level items, but each discussion has it's own XML feed generated so you can keep a folder in your newsreader for disposable feeds--ones that you could ditch at any moment when the conversation no longer interests you.