What about overdubbing functionality for the sequencers?
Enter overdubbing mode with shift rec
note played will be stacked on a layer on top of the existing one
added functionalities:
[keypress1 +] step buttons allow to mute, unmute and clear layers
[keypress2 +] step buttons allow to clear layers
[keypress3 +] step buttons to choose which layer is displayed on playing on step buttons
prerequisite: polyphonic sequencers
