Just an idea for buttons on arranger keyboards.

There should a row of 8 programmable buttons. So you could program them for the functions you need. If you need a button for maunal bass on/off, you could assign that function to one of such buttons.
This way a player can get dedicated buttons for the function they need the most.

it's somewhat like direct access button combination in PSR2000, only more customisable and using a single button click.

If an arranger board has nice sounds and good customisable interface, it will be a hit.