>>> But more importantly, current screen technology requires the driver to focus on the surface of the screen itself, which is mere feet away from their eyes. This is a large change in focal distance from looking at the road ahead.
If you’re over the age of 40 or so, it takes time, a few hundred milliseconds at least, to refocus your gaze distance. A screen is near. When driving, you’re looking far. A mirror is something to glance at.
I test-drove a Polestar with a screen for a rear-vision mirror (and no actual rear window) and it was completely undrivable for me. It takes longer for my eyes to refocus on the near distance than I feel comfortable removing my gaze from the road ahead. I turned around after 10 minutes and returned it to the lot.