For my friends on console, Key change presets. Right now we have the D-Pad and Face buttons mapped to C Major, with Shoulder buttons to play flats and sharps, and triggers to switch octave. That works great, unless you want to play anything in any other key signature. Being able to quickly transpose every button up or down to a different key, and switch from Major to Minor would be awesome, but would require at minimum one more octave added, preferably two with a range from A2 to A7 instead of the current C3 to C6.

With regard to the instrument voices, Piano definitely needs a rework. Right now it sounds like it has a muffler constantly applied or something. The notes fade after a single second no matter how long you hold the button down. That's not how pianos work. I can go over to my own IRL piano and press a key with the lightest touch, and it will ring out for at least 8 seconds before it has faded out completely. When playing at a regular volume, it can take anywhere up to 20 seconds for a note to fade.
I saw someone mention the putting the mode switch from the electric guitar onto other instruments. They can keep the old piano sound and rename it Muffler, then add Regular, Sustain and Una Corda modes.