Not sure about the feasibility of this, but it'd be interesting to be able to have ZC play multiple music tracks at once, whether that be MIDI or Enhanced Music, as well as allowing at least ZScript to control each of them separately. Would allow for some (basic) dynamic soundtracking (fading between different versions of the same track, having one play quietly in the background while the other is the main thing, etc.)
Also, I forget if volume control on music is already an implemented feature, but it's almost a must if we're allowing multiple music tracks to play at once.
