What Google would have to do is participate in some sort of standards body for ads, like the IAB except with the sole purpose of determining "compliant" ad comp

What Google would have to do is participate in some sort of standards body for ads, like the IAB except with the sole purpose of determining "compliant" ad companies vs ad companies who will be blocked by default. If they can get enough buy in, then they'll implement adblocking in Chrome while saying "we're not using monopoly power, we are simply implementing the standard X that Internet Explorer, Safari, Opera and Firefox have all implemented before us".