@Fab
Either way, bloody good work!
Video elements can actually be embedded in canvas, which means they can be transformed at will (for instance rotation, see http://people.freedesktop.org/~company/stuff/video-demo.html for fun), and there are of course players that add transparent controls over the video area (like vimeo).
Having just watched that, I would say texture surfaces make even more sense for video playback in the canvas:
1) Rotation is trivial as you are just applying a texture to a transformed rectangle.
2) You can have as many as your graphics hardware comfortably allows, whereas overlays tend to be more restrictive
3) Rendering above and below other elements is no longer a problem.
I realise that this would involve quite some work, of course.