Not sure I understand the question exactly. Generally, a file picker UI could look exactly the same in VR as it does out of VR, just projected on a flat surface.
The crucial point is to remain inside the stereoscopic VR view since exiting VR is very disruptive.
Any chance this PoC file browser is open source and available? I've been looking at these changes and I'm not sure how I should handle discovery of new devices, e.g. insertion of a new SD card, or an OTG USB device.
The crucial point is to remain inside the stereoscopic VR view since exiting VR is very disruptive.