Android 7 is out today for select Nexus phones.
For now, we know there will be some kind of accelerometer and gyroscope performance metrics OEMs will need to meet. For the display technology, Google has said that AMOLED displays will be a requirement — no LCDs allowed. Phones will probably also need to meet minimum performance requirements — ARM and others are beginning to design mobile SoCs with VR performance in mind, so finding high-end phones that meet those requirements should be relatively easy.
Some interesting details I didn’t know about Daydream VR in the linked section.
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