The key metric for me is how much information I can access with input under a minimal threshold. From personal experience, a hotkey to swap virtual desktops (e.g. Alt+Up) still isn't the same as having multiple physical monitors to reference.
However, I'd expect VR head orientation changes to look at different monitors to be fairly similar perceptually to what I do now, since it's the same physical action.
The bigger problem for the seat-tray problem is, afaik, both Oculus and the Vive use externally located tracking devices. Would be curious whether a fuzzier, internal-sensor-only, limited "intent" tracking mode (e.g. flick head to switch monitor) would make people hurl or not.
Yes, it would. This has been studied pretty extensively, the head movements need to be very precisely matched by rendering. The absolute worst you can do is any kind of non-linear response -- acceleration + lag can make people who are very tolerant of VR nausea literally throw up.
And use it on any sort of system that can show the outside world (AR, or pass through camera in VR) and it goes away completely.
Gesture interfaces could work.
If you don't experience it, good for you, you are one of the lucky ones.