I love the idea of this editor. Unfortunately the WP plugin has two killer concerns in my opinion:
Unlike the on-line demo, there's no way to edit the plug-in functionality (e.g., adding buttons or resizing it) other than editing the code. I don't have time for that.
Most importantly, inserting video or images is very difficult; it doesn't play well with WP.
I believe the WYMeditor approach is brilliant thinking. It's just not ready for prime time as a WP plugin.