I think pipe organs have shown, historically, that multiple "keyboards" do work and can be ergonomic. In fact, that's what I based my comment about slanting keyboards on.
I think the ideal minimal setup requires two keyboards, one weighted, one "not so much". Playing organ parts on a weighted action creates the wrong mindset. You can't "flip" your fingers around the keys. Organ playing also requires shifting fingers smoothly to new keys while holding other keys down. Not as easy on a weighted keyboard. At the same time, it's very difficult to do octave runs cleanly on a non-weighted action. Semi-weighted actions are a necessary abomination. What's really needed is an action that uses momentum rather than springs as the opposing force. I'm pretty sure we're going to see people's hands ruined by stiff semi-weighted actions.
Multiple keybeds and volume pedals have also been a way of getting around patch changes, again, as in pipe organs.