In reply to Nick Halsey.

This all very disturbing news, Nick. The way you are describing it, the Customizer becomes this huge section filled with bloat from all plugins (that do something to the frontend).

What is happening to the freedom that WordPress used to offer? What's with pushing people into a corner? I get it that some standardisation is needed (theme options), but why add plugins and menus to it?

How about plugins that do something in both front- and backend (let's say WordPress SEO by Yoast)? Ram it into the Customizer? That obviously is not going to work!