Fun idea! The note mappings shown at the end of the article seem quite specific to producing the code written for the demo, but I could imagine a more general mapping. Velocity also allows for some interesting possibilities, such as uppercase/lowercase. Rather than mapping chords to individual letters, notes could map to letters and chords involving those letters could map to common patterns with the letters as mnemo…
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 )