Multiple instruments on one staff
This feature would make it a million times easier to make condensed scores sound good. The idea is to be able to pick two different sounds for a single staff/part and designate a voice for each sound.
For example, if I wanted a Flute/Oboe split on one staff, I could assign MuseSounds Flute 1 to voice 1 (blue), and MuseSounds Oboe to voice 2 (green).
There are probably some programming issues that would come from this that I wouldn't know about, but it would be nice for people who compose/arrange for band and orchestra.