With the Front-end Editor using the Customizer as a framework, I wonder if the interface will look similar to this experiment? I hope not.
This plugin is really a prototype to demonstrate how the Customizer can be used to preview changes to posts/postmeta at an architectural level. Hardly any consideration has been given to UI, which Avryl has been doing a great job with in her Front-end editor.
Ultimately, I’m interested to see how the Front-end Editor comes into play when previewing a post or writing a draft post. Will we be able to use it to write a post or will the editor be refrained from use until after a post/page is published?
You can use this Customize Posts plugin to edit drafts as well. Just create a new post post, save a draft, and then click Preview. You can then click Customize in the admin bar to then access that post from the Customizer and you can make changes, including transitioning the post draft to a published post. This relates to a previous prototype I worked on in the Customizer Everywhere plugin, which replaces the “Preview” button with a “Preview & Customize” button.
In this case and as I’ve seen mentioned already, editing should be done inline and not with boxes popping up around the content.
In terms of a prototype which demonstrates how inline editing can be added to the Customizer, see my other prototype: Customize Inline Editing.