Musocity... looks nice. Ideas, sure. I would rather see condensed simpler filtered picker similar to ones found in Halion, Synthmaster and many others.

#1 Task: The work must be done to sift through the jungle of PGmusic MIDI styles to find better stems.
A good start, in my opinion would be extract 300-400 usable piano and related stems from styles, rename, index them etc.
The good news, this doesn't require much knowledge in programming, just a pair of good ears, so even a PGmusic intern can do this kind of work.

My main issue is this. Most of us own the content, it is there! But almost no one uses it, simply because the workflow is absolutely awkward.