Just stumbled over an article, very vague, but promising. Apple highend VR headset
That fits to other articles like RUMOR: Apple AR/VR Headset with 8K Resolution Per-eye here dated from Oct 2016.
There seems to be something behind. In combination with new designed own chip like M1 it may be possible.
Imagine 8K per eye, own graphics kernel per display, expected big FOV.