amp4email is open for anyone to support, and per https://blog.amp.dev/2019/03/26/building-the-future-of-email... it's supported by Yahoo Mail, Mail.ru, Outlook, and Gmail. It's not comparable to IE-only features.

(Disclosure: I work for Google, speaking only for myself)

Christ. If that's "the future of email", I'm going back to writing letters.