@anildash I think the 'just a display' idea is quite interesting. How cheap could you make the system if you just wanted passthrough and some fairly basic 'display something on some flat panels in VR space' functionality?
I know Apple isn't in to cheap, but if you can put a single much lower cost processor in it, and only have enough sensors for passthrough and basic head tracking (no hand tracking at all), perhaps it could be the $700 display that you can use with all your iDevices?