The proposed implementation revolves around a new base class which maintains a registry of overlays;
it can be improved in a couple of points.

1. If a user opens an overlay (eg. a dialog) and then changes story in Storybook, the overlay is not removed from the registry and it's still considered opened (isOpen=true). The usage of the WeakRef API could (in theory) solve this issue; however I tried to force the garbage collector with the Chrome Devtools console and nothing happened.
2. Related to previous point, since it's possible that the stack is filled with old overlay's instances, hitting ESC with no visible overlays will call the close method on old instances. Could it lead to issues?
3. The cleanStack method will work if the overlays are not reused (e.g element with the same id in different pages) and will not work for overlays in the ShadowDOM

A proposal discussed with @TomMenga could be to not maintain a registry and to simply use event.preventDefault combined with the check on event.defaultPrevented in all the keydown function on ESC hit.