This is very bad. I work in a large company, we have several installations where wp is the backend and frontend is an iOS app or a decoupled web application. I believe that this approach will become more common as wp-api getting better. Pushing more settings and content editing to the Customizer (requiring a traditional theme) will block this development and move wp to a big monolith, when the rest of the world needs smart, decoupled api based microservices. Simply wrong direction.