"Doing an IE6" for Google would be quite different from what Microsoft did, who wanted the desktop to stay relevant. For Google the web is just an advertisement platform. If/When Firefix is gone, they will hold all the cards. "Doing an IE6" might mean removing support for ad-blockers. Or making Google DNS mandatory. Or have everything you do on the web be phoned to Google, to improve your advertising experience. Assume they will find creative ways to monetize the web, ways that we didn't even think of yet. If you thought the web in 2019 was bad, beware of the Google Future.
AMP seems to be an example of the kind of web that (some parts of) Google wants. Hosted on their servers, transformed by their tools, commoditized and sanitized for ad insertion.
Today when you navigate to google.com from Microsoft Edge, there's a barrage of popups urging you to use Chrome instead.
When Chrome is completely dominant, maybe those popups will be on non-AMP sites urging you to "get the best experience"? It's guaranteed that there will be a lot of internal pressure to use Chrome to promote the goals of other divisions at Google.
Why did MS want to do an IE6? For power and control. You imply a difference in your statement, but it's only a matter of time before it becomes too seductive to resist.
It only needs to make sense in the minds of a handful of high-level managers, and we all suffer.
