My gut tells me that they can’t effectively add (in a pure fashion) on top of your existing Internet connection with 100% segmentation. Instead, they found a clever way to do the effectively the same, but still effects some of the traffic during peak loads.

What they really need to do is modify the cable modems so they can handle multiple streams (‘channels’), one for general Internet use, and various additional ones that they want to prioritize but are dedicated for the purpose. I personally don’t see the issue if they do it that way. The just need to fully segment stuff — just the same as having video on your cable doesn’t effect your Internet, neither should have Xfinity on your XBOX.