[deanhills]

Looks promising but in practical situations it looks like more of a huge headache. Editing system they have now is simple and straight forward. This system seems heavily relay on Ajex and html5 so it will be a problem for old computers. I wish they would do this change while keeping the old editor.

Agreed @xdude  If the change was going to make an enormous improvement beyond what we're already getting with the Customizer and some plugins, then OK.  But this may break some really quality and classic paid themes.  Thing is that WordPress is not a perfect script already.  The addition of a plugin in itself can create problems.  So I think there are plenty of users who are going to wake up with huge headaches.  As I imagine no one is going to do their due diligence and test it before the update is launched.  And few who are on automatic updates are going to think about changing to manual.