I've got a great real-world example of why fast lanes won't work.
I spent a night at a 'hip' hotel in West Hollywood. Room, with tax, was $308.
I thought I'd catch up on some episodes of House MD on Netflix and had utterly horrid quality. I did some speed tests (testmy.net) and saw I was being shaped down to 500kbps. I had better speeds while stay at some backwoods motor lodge in Minnesota recently.
I called reception and they informed me that they offer "super fast internet" for only $14.95 more.
Effectively they are capping their internet and offering to uncap it for a premium.
That's why fast lanes don't work.