that toolbox should allow the user to select the appropriate clef for a track; this allows the score editor to use the wanted clef instead of defaulting to "grand staff", which is pretty space-consuming

the toolbox should have three entries:

maybe later more clefs get added, but that's enough.

class Track should have a enum staff_type { TREBLE, BASS, GRAND_STAFF } or so which is accessible from the editors;

shouldn't be that hard if you are familiar with that part of muse ;)