At work, I just had to test all VR options, mobile apps, etc including Google Cardboard. The short of it is that the best experience is to be had on Android phones and Windows PCs for now. Apple has no answer other than paving the way via APIs in iOS. I had the company compromise and buy VR tech that is cross platform and can be exported easily and compatible with Cardboard type headsets. I hope Apple decides to answer soon, even if it's something tepid like added features in the Video player and a headset added to the Apple Store.