I would draw a parallel between this notation and guitar tablature. Unfortunately, all professional guitarists (and especially classical guitarists) that I know prefer traditional notation to tab. I personally find tab terribly hard to parse (disclaimer: I'm a classically trained musician). I think that the proponents of Hummingbird will need to somehow address and overcome this idea that "real" musicians only read "real" music. Overcoming an entrenched standard, especially one with hundreds of years of history is a terribly hard journey, even if you're only aiming at a tiny fraction of users.

I also have quite a few quibbles with the specifics and usability of this notation, but this is not the place for that.