Target Audience
First of all, let's clearly identify who is not a target audience. As described in the "Great Challenge of Breaking Tradition" page, there is really no point in trying to sell the idea to those who can already read music. And why would they be interested? Furthermore, if one wants to participate in the mainstream of the music world today, one must speak the language of traditional notation (unless you can manage your musical career goals via playing by ear*). So those who are dedicated to a “serious” path in music as a professional, a dedicated enthusiast, or an academic are likely going to need to be able to read it and therefore are not a target audience.
But here are some candidate players who just want to enjoy making music for their own pleasure:
Younger students of music who want to play in the marching band, jazz band, or their own garage band.
Adolescents and adults who want to play for their own enjoyment, alone or with friends and family.
Retirees who want to fulfill a lifelong desire to make music.
People who gave up learning to play an instrument because of the difficulty of reading music and would like to try again with a simpler notation.
Those who are not sure whether they really want, or are able, to play music. If reading sheet music weren't so difficult and time-consuming, then perhaps they could just give it a spin and find out in short order with an easy-to-read alternative notation.
People with visual or cognitive disabilities who find they cannot manage the complex mental processing of irregular octave lines, key signatures, and unintuitive duration symbols required by traditional notation; a simpler approach might be all they need to move forward.
For some, the challenge of reading traditional notation slows down the learning process to the point that it can take all the enjoyment out of playing. For most of these amateurs (and I mean this in the positive sense of the word's French origin: lovers), there is no need to needlessly suffer when an alternative notation can reduce the frustration, speed up the learning of music the student loves, and bring joy into making music.
And finally, I'm going to add music instructors to the list above. Not for their own use (after all they're already in the "club"), but for the sake of their students. If less frustration with reading sheet music leads to more enthusiasm about playing an instrument, then why wouldn't they want to use an alternative? Especially, if a student would just give up playing otherwise. And maybe successful students will continue to take lessons long term, and tell their friends. So why wouldn't instructors want to attract and retain more students?
*There are many famous professionals musicians who have/had difficulty reading music, or can’t read it at all, such as Prince, Eric Clapton, Elvis Presley, Paul McCartney, Bob Dylan, Jimi Hendrix, Dave Brubeck, Irving Berlin, and Joni Mitchell. Of course, these are the exceptions to the professional musician “rule”, but they illustrate that the challenge of reading music is not limited to beginners.