This has been completed: http://blog.castroller.com/2009/02/new-feature-share-to-a-single-user/

We will be adding the ability for multiple people to edit the same channel. But we probably won’t allow users to add to any channel.

Perhaps I’ll allow the owner of a channel to open up their channel to allow anyone to add it it.

Good idea, it would let many more podcasts get categorised without relying on the editors of the site.