Implement Custom VR SDK

Hi,

To implement stereo rendering in Unity we have to add a stereo SDK (Cardboard or Vuforia).

Will it be possible in the future to implement stereo rendering without using an underlying SDK, while still benefiting from Unity's optimised approach?

1. Cardboard would be great, but takes control of the camera which we don't want.
2. We have a custom implementation, but want to use Unity's higher performance implementation.
3. Custom stereo rendering appears to be buggy / isn't able to be integrated with single pass stereo.

Is there likely to be support in the future for adding custom stereo / VR SDKs, or will it be possible to render to two views via Unity's single pass rendering (while defining custom distortion etc)?