My drive to make an isomorphic keyboard comes from my limitations. I have painful joints that can make playing regular musical difficult. 

• I can't hold items of any weight for long so that eliminates wind instruments, guitars etc.
• Playing percussion jolts the joints causing pain
• Limits to how wide I can spread my fingers without increasing pain - this means piano keyboards keys are just too far apart
• Stringed instruments often have very contorted hand shapes to hold down the notes - not pleasant on my hands

Using a grid of keys in an isomorphic layout should be better for me to play

• Keys closer together for less stretching
• Chord patterns that require less twisted hand shapes than a regular piano keyboard
• Potentially a smaller, lighter keyboard