In reply to Bud.

Customizer is built on backbone which is near dead : https://trends.google.com/trends/explore?date=all&q=backbonejs , should WordPress use it : Definitely No. With full site editing in place who needs a Customizer. I am developing Blocks and theme on the new WP and it is really awesome. You can directly add CSS to the page using the raw HTML block. The Custom CSS feature which is being missed so much was already a wrong way to add css to pages. If there is css which has to be applied to all the pages of a site it should added in the style.css of the theme, not as an inline css.