Most of the large CDN's already deliver straight into Comcast's network. Last I heard Netflix was already paying Level3 to do this. Xfinity doesn't have a magic pipe, all the content and deliver is internal to the Comcast network so its its own "CDN".
I don't really want to rehash that whole discussion, but Comcast admits they're using DiffServ tagging. People are just debating whether it's a form of "prioritization" or not.
