This is the basic working principle of the stenotype, which enables extremely fast typing (200wpm+) but needs a lot of practice to learn. A MIDI keyboard does seem like an ideal input device for this, if anyone wants to take this idea further they could try to make it work with Plover (http://stenoknight.com/wiki/Main_Page )
Then again, many more people have midi keyboards than steno machines, so it might be worth the try to adapt it for plover.
An even more awesome idea would be to use something like the EWI or the Eigenharp pico as a steno device, since those are more portable than either a midi keyboard or a normal keyboard. Not sure about the Eigenharp, but for the EWI you'd have to use another firmware (than the current one which translates fingerings into single midi notes and doesn't support chording), which sadly puts it out of the frame.
playing the piano i would often struggle with not enough finger opening/movement.
i seeing how slow he 'typed' that code, i think the other way around would make more sense. i.e. learning the piano with a matrix keyboard.
We just need pressure sensitive switches. but after that, you would get much more agility. not to mention be able to play pieces that are impossible without 4 hands.
In addition to @JoshTriplett's idea about velocity, I guess knobs and faders might have some interesting applications too.
P.S. Btw, it's a "she", it's my colleague performing :)
(P.S. you can't really call it C# minor if there are no cadences, ya know, in C# minor.)
Still looks like fun, though.
and also by experience, one should know that everytime you press that many w, you WILL type a b or h :)
That's it, I'm writing a plugin that plays dubstep while you type.