I put Mugician up on GitHub. All I ask is that anybody trying to use it, don't confuse people with what you build. I would prefer that you submit sane changes and bugfixes for the official build. But if you want to do something wierd, then it will have to go into your own instrument. In that case, give credit to Mugician for its lineage. Give it your own name. Give it your own app id. Most of all: Make sure that there isn't something about your app that breaks Mugician builds that users will already have on their iPads.
I am working on a different instrument now, but I think for historical reasons, and people who would simply like to make derivatives this is useful. Mugician's code isn't pretty. In some respects, it might be the worst code I have ever written (theoretically, in a pure software engineering sense). But it did get an incredible amount of craftsmanship in getting the details right as far as sound,latency, feel under the fingers, etc. That's why it looks like some clay that has been stretched and pulled endlessly!
It was a rush job, but it served me really well in the real-world. It worked out so well, that having it has been a sort of addiction that prevented me from having a next instrument; or more importantly, prevented me from caring about what anybody else wants.
I am working on Pythagoras now, which is similar to Mugician, and uses the same sound engine (which I had to pull out and clean a little bit).
Note that this source is not exactly like the build on the store. I hadn't been bothering to commit and tag builds when I was working on it. There is also something that needs to be commented out for anything that you plan to submit to Apple.
Contact me: email@example.com