The other unfortunate outcome I immediately foresee is that by adding an element of risk to visiting a new site (of wasting money on something useless, even a tiny amount), people will be even more inclined to stay within walled gardens they already know rather than explore the internet. This takes a problem we already have and makes it way worse.
I'd bet it goes down to 0 for 99%+ websites. A few big websites might keep it, but anything that inhibits the site from generating (meaningful) data, like users posting, sharing product feedback, describing fun things to do, showing pictures of an area, etc. will be reduced. What I am betting on is most sites opting for monetizing as data generation, rather than ad serving.