my primary instrument is the accordion, not the piano. It would be nice if a couple of additional features were added to Musescore specifically for accordion. The first that springs to mind is that by default everything in the accordion Bass staff (left hand for the musician) is stacatto by default. It would be nice to be able to set this as an option when the instrument is one of the accordion types.
Secondly, under the Bass staff I put the button indicators. This uses the same text as Chord Text, but goes under the staff instead of above. Additionally for the Bass staff it uses a dash like a Tenuto, or a double dash like an equals sign to signify which row the button required is located in (fundamental row, counterbass row, or extra row if the instrument is configured French/Bassetti style rather than Italian/Stradella). (Unlike a piano, an accordion has redundancy - you get exactly the same sound from different buttons.) It would be nice if button indicator text was available instead of having to cludge Chord Text.
Thirdly, it would be nice to be able to adjust the volume of the Bass Clef and Treble Clef independently for accordion. These are independently adjustable on Roland electronic accordions. I'm sure that workarounds for this problem exist. But it would be a nice feature to have available.