Higher resolution displays will be a big improvement, even if they use scaling from a lower resolution to drive the display. The big flaw with VR right now is the visible sub-pixels. Even 720p per eye would be better than what we have now, if the subpixels could somehow be hidden.
ARM, Imagination, and Qualcomm have all begun optimizing their GPUs for VR and Google's Daydream platform.
I wonder if Vivante is intending to play in this space.
Mobile VR is going to require an external power source. Otherwise, it'll be a very short experience, indeed. That would pose its own problem, as most USB cables are only a couple meters long, and the long ones don't seem capable of supplying much current. Perhaps the standard solution will be to plug into one of those USB power bricks, while it warms your pocket.
Also, I think we might start seeing more metal-backed phones, as bigger mobile GPUs will need to dissipate more heat, when running flat out for extended periods of time.
In spite of all the enthusiasm, mobile VR is going to lag behind PCs, badly. The gulf in GPU performance is too big, and it's mostly a function of power (as in Watts). Mobile has a limited power budget, and getting rid of it (as heat) is already a limiting factor for mobile games.