Daft question: would it be possible to attach an accelerometer (edit: or gyroscope) to the monitor and connect it to a script to update the display angle on the fly?
Yes but swapping the angle is not an instant action. In fact it has a huge black screen flash and takes like 10 or so seconds.
I've wondered why that is. Both Linux and MacOS take several seconds to change low level screen parameters like this. It made some sense in the age of CRTs, but today I struggle to understand why it takes more than 50ms. What is it doing during all that time??
I'm guessing It's stopping and reloading services that don't have any support for for runtime changes
You could easily have instant and smooth rotation like that in a Wayland compositor.
Yes. Linus personally added the driver in the next release of the kernel.