I had the opportunity to ask Palmer Luckey (the founder of OR) directly about the possibility of smartphone based HMDs. It turns out he's looked into it quite a

I had the opportunity to ask Palmer Luckey (the founder of OR) directly about the possibility of smartphone based HMDs. It turns out he's looked into it quite a bit, but ultimately the unsolvable latency of the sensors made him move on. It could work for viewing 3D content or for situations where the head will only be moved fairly slowly, but it's not a great solution for most applications. I would note that a dedicated handset maker could create the hardware and drivers which fix this.