All people have to do is speak with their wallet. If there was sudden mass migration from Comcast over this policy, they would surely pull back on it.
Problem is, people will piss and moan, but how many will actually leave Comcast over it? Anyone? Probably those who have U-verse or FIOS in their service area, which would likely amount to upgrade anyway.
How many will take a stand and go back to DSL,Wireless, Satellite or Dialup in order to send that message to Comcast?
cue the chirping crickets.
Yet, if Comcast does get away with, without significant subscriber loss, other providers will likely follow suit.