I would like to propose the deprecation of the Appearance > Widgets screen in favor of the Customizer > Widgets Panel.
In MHO the screen is counter intuitive and counter productive for what it does. My main reason for the proposal is that many themes are moving away from the typical “Sidebar” to what I call Widgetized Locations and the Customizer handles the return of available locations (per template) instead of the whole lot in one place.
Alternatively link and focus the submenu to the Customizer Panel just like how the Header and Background (where a theme supports them) are linked.