The way this has always works, and is not changing based on anything 'network neutrality' related, is that generally the sending network (Netflix) pays the receiving network (Comcast) based on something like the 95th percentile of their sending rate. It maybe not be linear, but if Netflix starts sending 2x traffic, they will pay something like 1.8x-2x. That's not changing, and nobody is disputing this.
What we're talking about here is that Comcast could take a user's 20Mbps connection and decide that even though it's fully provisioned in the last mile for 20Mbps, and they have plenty of pipe to get the Netflix data to the Comcast side of the last mile, that Comcast can just decide that Netflix will only get 5Mbps of that 20Mbps, that is unless Netflix pays the ransom money to Comcast to change that arbitrary limit.