I'm not expecting this to actually happen... but I would instantly buy a Mac laptop that let me physically separate the screen and the keyboard while continuing to use them both. Then I could set the screen up on a portable stand at approximately the right height and distance while the keyboard lived closer to me and lower down, perhaps even in my lap.

Right now the best I can do is to carry an external keyboard. But it's a pain to have to tote around redundant hardware. Of course, it's also a pain to be in pain after spending too much time using an un-ergonomic laptop.

The main limiting thing there for me that's annoying is that Mac OS seems to require me to use my laptop's screen as the main one putting the menubar there instead of on my larger external monitor.

same here. and I know some use there laptop screen as a second monitor. so this is a bad idea on many fronts.