HTC Vive definitely looks like the best PC-VR gear.
Google Cardboard viewer-to-PC support shouldn't be too hard to add through Unity with a free plugin like Trinus (a fairly popular method of streaming from desktop to cardboard and getting gyroscope data back/etc.): https://www.assetstore.unity3d.com/en/#!/content/43781
Even just rendering SBS (Side-By-Side) there's other streaming apps that take care of it from there.
Perhaps it could even eventually run natively as an Android app with a bluetooth controller like the MOGA Pro (should have decent performance considering the hardware of newer phones? Eg: I can run Quake 1 in VR at a high speed on an LG G4, Open Arena, open source Quake 3, even runs on it although at a lower framerate).