Do you mean that Fox in general is going to become a cable-only channel and no longer a free over-the-air network? Or just that they will require you to have a cable or satellite subscription to watch their content online? (I wouldn't be surprised by the latter; they already moved to a model for online streaming that allows DISH network customers to stream shows the day after they air, whereas non-subscribers have to wait 8 days.)
I don't mind having to wait a week to watch a new episode, since I'm usually behind anyway, but there's no way I'll pay to watch free network TV online. I don't care enough about TV to pay for it, which is why I cancelled cable TV years ago. I pay $50/month for my cable internet, that's enough.