Even regardless of me being pro-AMP or anti-AMP, I'm not sure what you're trying to get at here.

- Google has settings for search and a page for these settings. For example, I have sometime in the past went to that page and set my preferences there. And now they're taken into account when I use Google's search. Like settings are wont to do, y'know.

- We already know how search without AMP works.

I think you're approaching it from the wrong POV. First of all, the option needs to be on the site owner/developer side on whether to adopt AMP or not - and not have the decision of not adopting AMP adversely affect search ranking.

As a user, I should just see whatever the site lets me see. If they decide AMP is best for user experience, I would no doubt get it. If they decide to show a responsive mobile friendly site because it works best, then show me that.

My first guess is to only make it available in the first place to people using search while signed in. Could even sell it as a way to get the “faster” web by signing in. At least that way there’s a choice.

Making it default for everyone and then forcing people to sign in to opt out would be counterproductive from a privacy standpoint.

Could also just provide the original link right next to the AMP link in search results and let users decide.