It's not possible to allow user-supplied plug-ins with most or possibly all of the app stores. Certainly not with iOS, or WinPhone, and probably not with Android, either. You know, sandbox and such, can't load unsigned code that's not bundled with the app itself.
You're welcome to point out a contradiction to that. I suppose it would be "OK" if we told people they have to use an Android device if they want to supply their own plug-ins.
You can ask Peter to add configuration options for various inputs, such as sample rate, resampling method, ramping, etc. Just don't expect the options to be all that great. For instance, you technically can enable sinc interpolation, or band limited synthesis, but they'll both be incredibly slow on portable devices.