If I understand, your experience is that changing a split while playing is too cumbersome?
Duplex keyboard mostly makes sense with grid controllers, using different layouts etc. and you can’t change those splits on the fly using that tool…
But it should not be hard to create a tool for managing all instr. MIDI assignments in a song using the standard input port(s). So, ideally you would be able to control the split note with MIDI, somehow. Have to look into our options here…
In fact, since Renoise is kind of ‘backwards’ (saves these settings inside the instrument, not the song) it would make a great deal of sense to have such a ‘performers panel’.
Perhaps I will take a few cues from this tool as well (the propagation part - it doesn’t do splits):
https://forum.renoise.com/t/new-tool-2-8-midi-management-console/35513