This looks like a really interesting direction to take the whole WYSIWYG editor functionality, making use of new techniques available in HTML5.
The user interface is much simpler than the traditional library but, for me, this is a feature, not a bug. It forces users to consider the foundations of their content rather than worrying about style.
What particularly piqued my interest is the speech input feature (currently only supported in Chrome). This opens up a whole new opportunity not just for accessibility but also mobile input (think Apple’s Siri).