This is actually a very nice concept.
The thing with mobile devices is you usually use them with one or at most 2 thumbs. This is fine for things where multiple simultaneous actions are not necessary, for example dialing a number or drawing lines. But as operations get more complex, i.e. zooming in, typing quikly, you need both your hands; Either one to hold the device and the other on to touch the screen, or your two thumbs while balancing the device in your palms.
The approach we see on that video solves that problem. I'm sure Apple has something very similar in development. An easy way to realize this would be to have 1 multitouch display on the front and one multitouch surface (no need a display on the back...) on the back. This way, you can move your thumbs out of the way to see the whole display. Like it is now, the button on the iPhone you touch is covered while you touch it so you find yourself moving your touch hand away to reveal the screen every time.
The transparent touch screen sounds noce at first, but then you would have to hold it against a bright background to read anything. I agree that having the touch sensor only on the back side is bad, but having it on both sides is pretty awesome. I'm not sure I need to see my fingers all the time though, the cursors should suffise, maybe in different shapes to distinguish the fingers. Maybe an arrow that is parallel to the finger that controls it.
