This is great!!! For me, one of the greatest advantages of WordPress is the tightly integrated Wysiwyg and shortcodes api.

The big weakness of shortcodes has always been that they are very scary for your average user, serving to actually make the editing process far more complex, which is a shame when the Tiny MCE integration is so tight and user friendly.

As a developer / designer I often have to use some interpretation of custom fields instead of shortcodes to keep the editing experience streamlined. Custom fields can often be a bit heavy for a lot of purposes and some kind of lightweight and visual shortcode interface is much needed.

I really, really hope something like Shortcake is rolled into core at some point.