With the billions in profits and considering that Senior Management at most ISP's net millions of dollars a year in salaries and perks, there is no reason to pay anything more than existing monthly fees for uncapped access. Fact is, Comcast charging $50 per month for 6Mbps down is too much to begin with.
Rather than squeezing customers for more money or setting up a tiered user/payment structure, the ISP's should dump money into upgrading their infrastructure.
Leave the enforcement of DRM, bootlegging, and illegal downloads to the proper authorities and do not force the ISP's into playing