"Maybe some kind of projected light field will be the next solution?"
already being done! http://en.m.wikipedia.org/wiki/Magic_Leap
Magic Leap is more of an AR solution, like HoloLens, as opposed to VR (as far as anyone can tell, seeing as they haven't demoed anything publicly).
Nvidia's light-field stuff seems to be more of a VR solution, but requires even higher pixel densities. https://research.nvidia.com/publication/near-eye-light-field...
Oculus has been riding the smartphone screen density wave but I'm not sure that will continue much longer since for phone use going beyond 500ppi doesn't make much difference.
Maybe some kind of projected light field will be the next solution?
GPUs will keep getting faster and smaller. Have you seen NVIDIA X1?