This is a beautiful video and a very interesting invention, but I find it a bit worrying that they don't show a single meaningful application for that technology.
I think the main problem with this input method will be the lack of feedback: how do you know if your input was properly registered, unless you're looking at your phone? And if you are, why not just use your phone?
One possible solution could be audio feedback: for example, I could see it being paired with a bluetooth headset that confirms the commands you enter.
It's a bit disappointing that the video didn't explore any of that though.
Wasn't April last month :s