Dick Costolo:

"[E]ven if we can all get along and agree on a common base syndication format and the number of different clients dwindles to a powerful few, the entire syndication space will simultaneously witness a growing sophistication and accompanied level of fragmentation through conflicting namespaces and specialty clients.
We are already seeing the emergence of one such example. Apple has begun syndicating genre lists and top songs via RSS for their iTunes service. If you look at the xml behind an iTunes RSS feed, you will see that Apple has created an RSS extension for “what it means to be a song”; the namespace is identified by http://phobos.apple.com/rss/1.0/modules/itms/. It contains extensions like and to name just a couple. This extensibility is precisely what enables the syndication of rich media. Current RSS readers may not do anything with the itms namespace, but that’s ok, because Apple also reuses existing base RSS tags to display things like the name of the band and song and a link to the song at iTunes.
Will such a fragmented set of namespaces on top of a base format or perhaps even fragmented namespaces on top of conflicting base syndication formats cause the promise of syndication to collapse? It need not. The beauty of syndication is that it’s still all xml underneath, and where there’s an underlying structure, there’s a general ability to reconcile conflicting structures."