In reply to johannesf.

That's a very good point.

I have no real for/against opinion that is strong enough to warrant me coming out with a definite view as yet, but I think your point about using WordPress as a backend to a web application (which is one of the big talking points about the forthcoming REST API) is going to problematic if certain areas of the admin are only editable via the Customizer which would require a front end theme.

The is no harm in integrating Menu Management into the Customizer as an alternative way of managing menus visually, but all 'content' (including menus) must be manageable via the admin so that the admin can be used in isolation without a theme if WordPress is able to say that it a suitable application framework?