On 26th March 2019, Google officially launched AMP (Accelerated Mobile Pages) HTML email

AMP is a framework created from HTML, CSS, and JavaScript that enables you to build a lightweight email with shorter loading time. The email recipients can interact with the content directly, like fill a form, RSVP to an event, or respond to a survey from within the email.

As an Email marketers, we have to use two different MIME types for creating emails for the HTML part (text/html) and plain-text version. Therefore, every email should have an HTML version and a plain-text version in the ESP. When it comes to AMP email, a third MIME-type will be needed. This adds to the complexities of executing AMO. If WCA do not add support to this third MIME-type, it is not possible to create or deploy AMP-powered emails.