Interesting plugin and I like your suggestions for improvements, Jeff.

I know I'm not the first to point this out, but it's always worth remembering that these previews are still only a preview for a certain width/screen/device//browser/use/etc. That's always a limitation plugins like this will hit.

For both this plugin and the Front End Editor plugin, I personally still wonder whether either would be as necessary if theme authors spent more time making accurate editor-style.css files. If the primary problem is that text is the wrong font/size/color, WordPress already has a way to handle it.

If this plugin is particularly good for something, it does solve the issue of previewing shortcodes.

It'd be interesting to see a similar plugin that tried putting the preview in a third tab of the editor (i.e. "Visual," "Text," "Preview) a la GitHub's comments.