i am aghast that there are people who have obviously been composing for a long time, giving another composer advice as apalling as "dont do it if it wont get played."
this is ridiculous advice in every respect. the only time this advice has a shred of legitimacy is when someone's livelihood depends upon it. "dont do it because if you do, you wont be able to feed your family"
if everyone abided by this philosophy, (yes im talking even about composing for obscure instruments such as the armonica) this world would be seriously devoid of a LOT of precious artwork.
i could list hundreds of artists who are revered in today's society who were despised/ignored/unheard of/had no hopes of being heard(seen, published, read etc)
what kind of world would this be if they had given up when the community around them said "dont do that, no one will buy it!" ?
honestly people, get real.
this attitude is unfortunately permeating every aspect of art and some great work is really suffering because of it.
to the OP, forget this ridiculous mentality and write EXACTLY what YOU want to, not what other composers tell you is passe, or "hopeless." you may or may not end up with a masterpiece, but you WILL learn something, and there is always the possibility that if and when such an instrument makes a comeback, it will get played.