I'm not an expert so I'll just give the basics that I know about. Instead of being a passive node on the network, the new cable box would be active as part of a packet switched network. You make a request and the stream is sent over the hfc network. Since the hfc plant is broken down with plenty of bandwidth to the nodes to the headend the only problem would be between the nodes and customers asking for video but with enough nodes you woudn't have to devote much bandwidth to video on demand. At least thats my understanding, never looked into it much. Head over to the engineering department and ask them 
Facebook
Twitter