What I described then was that I would like a tool that allows me to mix multiple feed into one. Everything comes in an RSS or ATOM feed nowdays, so there are so many possible uses.
Google Reader allows you to do just this in a very simple way. Just tag the feeds you want to "mix" with a specific tag. Then go to Preferences->Tags. See the feed icon next to your tag? Click on it and you will be presented with a few more options.
Click "email a link" and get the ATOM feed link of your aggregated feeds! You can use this new feed in other apps.
An interesting variation would be to aggregate the "Shared Items" of your friends into a new feed you can all use, something like a collaborative feed of things a group of users find interesting! (To do this, subscribe to all your friends Shared Items feeds, tag them with a specific tag, then make this tag feed public...