I work in the mobile game space. Games I work on aren't really suited for VR, but there are parts that could be turned into a VR experience pretty easily and convincingly.
Let's say I had a top-down 3D racing game. The gameplay and racing is handled outside of VR, but what if I wanted to allow the user to enter VR to view your cars in the garage? Or after the race, go to the finish line in VR and watch yourself finish the race.
When I build an app for GearVR, it asks me to 'please insert the device into the GearVR' which then boots the app. Is there support for nested VR like this inside a non-VR mobile application? I'm assuming not, but am hoping it's on the roadmap somewhere. Companion viewers would be a reasonable stepping stone if you could access game data from other applications, but it'd be neater to have it all in one bundle.