Layouts KCM
IMO previous decision doesn't cover all use cases of separate KCM for Layouts, for example layouts that exist without theme at all (similar how Splash screens now work).
They also don't overlap with each other as having more granular control for global theme in all aspects and maybe even show for user what components global theme sets also sounds reasonable.
So considering these points I'd like to propose and implement a separate KCM for layout.