Uncle Rupert (of the Skynets), Auntie Dido (of the TalkTalks), Uncle Richard (Probably not a real Virgin) and their ilk will be able to implement QoS (Quality of service).
Used right, this is a good thing, enabling live stuff like voice and video calls to cut in front of static stuff like document downloads.
This is a "Neutral" usage where traffic is prioritised by type, and already exists.
Non Neutral usage would boost one provider's content and potentially slow other provider's content making it less attractive.
This is a bad thing because most Internet Service Providers are selling "Quad play" solutions, where you get Internet, Telephone, Television and a Netflix type subscription.
So the technical guys at Sky might get a directive saying - Check the source IP addresses for streaming video, and stick it on the slow train unless it's one of ours.
It would be relatively simple to infer that this was happening, but extremely difficult to produce concrete evidence.
ie A monopolist's wet dream and a customer's nightmare.
The educated differ from the uneducated as much as the living from the dead. Aristotle