This is a great piece of design. I think, however, the vertical format really lends itself to a digital format only. Although you mention that these can be printed out, you effectively have only one double-stave layout per page. I would imagine that a song written in your format would take up a fair bit more paper than the traditional format. Also, you mention the use of colour, but if printed out in black-and-white, you lose that information. It may be obvious from the left-right spacing, but what if hands cross over each other (e.g. Bohemian Rhapsody intro)? Finally — on fast, syncopated songs, I could also imagine that it would be very difficult to see exactly where the not is supposed to be played, and therefore the performer may end up playing sections with the rhythm not as intended.
I still believe you have something interesting here. It would be great if you could have a think about how to optimise the design to take these issues into consideration. I’m very interested in reading any follow-up posts you may have about this!