Nice job. Quantizing to a given scale/signature controlled through touch or gestures to glide and create ambient textured soundscapes is actually a pretty well-explored space. I've seen some neat MPE-style ones that let you emulate aftertouch through haptic pressure and vibrato by wiggling your finger back and forth.

It’s a very popular genre of music apps on the iPad, since the larger screen lends itself well to this kind of musical performance. You should definitely check out apps like MorphWiz, GeoShred, etc. if you’re interested in this kind of thing.