Dave Winer writes: “Reading lists are OPML documents that point to RSS feeds, like most of the OPML documents you find, but instead of subscribing to each feed in the document, the reader or aggregator subscribes to the OPML document itself. When the author of the OPML document adds a feed, the aggregator automatically checks that feed in its next scan, and (key point) when a feed is removed, the aggregator no longer checks that feed. THe editor of the OPML file can update all the subscribers by updating the OPML file. Think of it as sort of a mutual fund for subscriptions.”
Cristian Vidmar offers more ideas.