That is, the idea they want is total bullcrap.
But it could be re-worked to act like this:
1) Build out infrastructure to give all customers speeds of 500 MBPS
2) Sell service to customers for speeds upto 300 MBPS. Make it clear that is what you are offering, at that price. You never advertise any speeds higher than 300 MBPS.
3) If however people are using content from approved fast lanes, you enable speeds upto 500 MBPS for content from those people.
4) Make a rule that if they ever choose to adverise speeds of over 300, they can no longer get paid for their fast lane service (and must pro-rate the money back if it was pre-paid).
THAT is something that most people would accept. Among other things, it would let the company upgrade their service much quicker if competition started coming around.
Of course, it would end up costing the ISP's a LOT more money than they make on the 'fast lanes', as actually have to BUILD the fast lane into their entire network, something they don't do and don't plan on doing.