I've been in contact with the developers of SoundPrism.
They have made some major improvements to the accessibility experience.
they've labeled all buttons and made the play surfaces direct touch, and made it so that VoiceOver announces or displays (in Braille) the key and related miner.
This is an app which allows the non-keyboard player to play chords, bass notes and arpeggios, and progressions very easily and intuitively.
It is based on a grid. The very center of the grid is the number 1 major chord in the key. Moving vertically up or down changes your chord. Moving horizontally gives you an arpeggio effect basically moving through inversions.
Chords are laid out vertically in rows. the center row is the major 1 chord. The next chord down is the related miner. Move down one more row and you have your 4 chord. Moving up from the center you have the 3 chord which is miner. Up one more row and you have the 5 chord.
the top of the grid is the 7 chord and the bottom of the grid is the 2 chord.
Put another way, in the key of C the chords are laid out thusly.
Bottom D miner
just above center E miner
Just above bottom F
Second from Top G
Just under middle A miner
Top row B diminished
and back to the middle for C.
Major chords are placed on alternating rows from miners..
anyway, if you haven't checked it out, you can download a free version, but I'm not sure if this will get the improvements.
You can turn off speech to play around, but if you like the idea, a MUCH more accessible version is very very close.
I like it so much that I will likely be using it to provide pads and drones when I lead worship at church.