If it is so much easier to use the Customizer, then why haven't developer's used it? There is certainly things that can't be done with it...

I have spent probably thousands of dollars on themes, most of the times because they offer advanced customization... Often, they are from individual developers (not a big company) and they will probably spend their time and energy creating new themes than spending a lot of time rewriting most of their older themes...

What will happen then? Their themes (at least the customization part) will stop working? I'll have to keep a copy of WP 4.2.2 at hand and not upgrade...