I have an idea, but it would go against net neutrality.
Have site based download weighting toward a monthly cap. For example, "legitimate" site likes iTunes, Netflix, Hulu, Steam, Windows update, etc. would have a 0.1-0.25 multiplier applied to data downloaded (1GB downloaded = 100-250MB toward a cap). While sites known to have a large quantity of pirated material would have a multiplier of 1 or more toward the same download cap. So users that play online games and stream movies from "pay-to-play" sites can download what they need and most likely not hit a cap and users who abuse the system will be penalized.
Just my two cents. And I know a lot of you here will say my idea isn't even worth that.