I forgot to mention the limitations of modern keyboards. I've always wanted a second row of programmable function keys that could be edited quickly as part of an OSD (perhaps even a small display on the KB itself for said purpose). I reckoned this would be minimally disruptive to the current ecosystem and yet offer most of what people need.

I haven't yet read Butterick's book. I was tempted to buy it the first time I visited his site but didn't. From what you say, it's time I did so.