It’s a simple but powerful use of OPML and a search engine to gauge popularity, if not a real-time method of gauging it.
There are going to be some amazing things done with data and feeds, this is just one of those uses.
How could this be extended?
One idea that immediately hits me is that a lot of people get overwhelmed with the amount of RSS feeds they subscribe to, and there is simply too much to read. Personally, I subscribe to over 100 feeds, so there is often an overwhelming amount of posts if I don’t keep up with my feed reading.
I’d love if my feedreader had this ability to quickly see the top one or two feed items from every feed I subscribe to. How handy would that be?