FORTHE NEXT little while, there’s going to be a steady, relentless drumbeat of expectation that an Apple virtual reality/mixed reality/ augmented reality headset is juuuuuust about to appear. There’s no doubt that such a device is in the works — Tim Cook has hinted at it, and we’ve seen signs of “realityOS” in other software. And obviously the technology exists: Apple makes advanced processors, there are the right kind of hi–res screens, 3D–sensing software is become increasingly advanced… so we must be about to see it, right?