There are plenty of ways virtual reality headsets could get better. They could offer higher-resolution screens (like the new Vive Pro), a wider field of view and improved built-in tracking sensors. But another feature might be even more essential: eye tracking. It's not a new concept -- we've been following FOVE's eye-tracking headset, as well as 7Invensun's Vive accessory, for a few years now. But it seems more important than ever as consumer VR winds up. Tobii, a company that's been exploring the potential of eye tracking for a while, is hoping to integrate its technology into the next generation of VR headsets. And based on some demos I saw, it's clearly not a question of if VR headsets will get eye tracking. It's when.