This is a kind of new musicology theory (which is very pompous of me to say) as well as an actual instrument
Nifty things like Rokebys Very Nervous System (view the super awesome link) or the Mistry gesture computer communicator remind me that certain gestures create moods thus you could have a musical
instrument that tends to cause a certain mood even though the composer uses it however they like
I like techno
thus
A version of Rokebys instrument that was centered around raising my arms up n the air n smiling a bunch (the researched smile that causes people to feel happy) would permit composition yet would make me feel goofy happy which certainly goes with techno
Its kind of the medium is the message yet the big thing here is that the instrument modality leads the composer
That could matter as the groups of gestures that people learn to make use of with gestural computing could be productive of various feelings or cognitions
Just as I have fantasized about rewriting the Tarot deck so all the cards were beneficial thus every Tarot reading would be pleasant If all of the gestures of a new kind of musical instrument were emotionally beneficial the compositions would tend towards beneficial
I know this is obvious from things like DDR or those leaning keyboardists yet I can imagine a slightly mermaidish version of musical instruments that always liked to be played rightly n lightly