AMP currently requires a meta viewport including the following values (at least):

<meta name="viewport" content="width=device-width,minimum-scale=1,initial-scale=1">

The requirement of minimum-scale=1 can be an impediment for adopting AMP, such as in the new default theme for WordPress core: WordPress/twentynineteen#199 (comment)

In the event an embed or other replaced element introduces horizontal scaling it's helpful to zoom below 1.0 to view the entire thing.

Apparently the initial reason for including minimum-scale=1 was due to a bug in Chrome that has since been fixed and it is no longer required. If that is the case, then the requirement should be lifted from AMP as well.

/cc @cramforce @amedina