Reminder that we've already had a spec for it. In the 90s! And it even has been implemented in the Internet Explorer: https://www.w3.org/P3P/ It did absolutely nothing for privacy. Google has been sending bogus P3P headers that broke IE's implementation and allowed all cookies. Adtech companies don't want users to have an easy opt-out. They didn't want P3P. They didn't want DNT. They will not want this new spec, unle…
I remember spending a silly amount of time trying to come up with a P3P policy that was both accurate and also didn't break sign-on for a single app that used multiple domains.