10up just released a new plugin called the Post Customizer. I, along with John James Jacoby, John Bloch, Drew Jaynes, and Carl Danley led the charge on the plugin. The idea of the plugin is to mimic the theme customizer for posts. The plugin adds functionality that displays an overlay when you click “Preview” within the post editor. The overlay has a sidebar allowing you to edit the excerpt and featured post. In the middle of the overlay is a frame that shows the front of the website. Within that frame you can edit the post title and content. This enables you to make “live” changes and to see how they look as you make them. There are other plugins that offer similar behavior. However, Post Customizer closely follows the Theme Customizer and thus WordPress standards.
We want to make this plugin super extensible, and we need all the help we can get. We would appreciate contributions! Fork the plugin on Github.