Are these sites a thing (small sites that can subsist on their ad revenue)?
If I couldn't pay the bills for one of my services, I would rather introduce a paid tier, or at least a paid ad-free version. Or I would ask for donations whenever the money runs out, like Wikipedia does.
A paid tier is a surprisingly narrow business model. People aren't willing to pay for much, and not every website has such an explicit product. A lot of that is just conditioning, as people aren't used to having to pay for anything since ads. And most people see ads as zero-cost. The second you start charging a dollar, now you're the guy charging the dollar that nobody else is.
How many forums do you pay for?
And donations are almost always a joke. Else you wouldn't have to beg in a way that puts most ads to shame: https://dl.dropboxusercontent.com/spa/quq37nq1583x0lf/nv9ad0..., and that's for a website that brings value to just about everyone that touches the internet.
What about all the small websites, from creative to forums, that aren't big enough to graduate from ads but can pay their own rent with them?
Seems like a net loss for humanity to lose them from the internet while keeping only the large businesses online.