In the indexing / catalog space, there's already Feedster. It's great for what it's intended to be - but it doesn't help me manage my subscriptions or filter feeds based on stuff I've already read, which was the real feature I need.
I waste my time already sifting through things I've already read, and I have a limited set of feeds that I look at. By expanding the scope of this service, you only compound this issue.
Then again, sounds a lot of the Microsoft software-as-a-service strategy we heard so much about. What's going on with Hailstorm / My Services anyways?
I still think I'm going to start working on this when I get some time. Maybe no one else would be interested in it, but the more I think about it, the more I realize how useful this would be for me.