In the course of hosting its inaugural Vive Ecoystem Conference in China earlier this week, HTC augmented its Viveport virtual reality marketplace to add eye-tracking ad tech devs can use in their VR games -- as long as they're free.
It's a portent of a more robust free-to-play VR industry, one registered Viveport developers may be able to make use of if they have (or are thinking about building) F2P VR games.
HTC's guidelines for devs looking to make use this "VR Ad Service," it seems that those who opt in to using it will automatically have their game or app's price on Viveport set to free. These ads can then be displayed in VR in a number of ways (from 360-degree video to embedded 2D ads [see below]) and are capable of capturing data like how often a player looks at them (if at all) and for how long.
Further information is only available to registered Viveport developers; game devs looking to become one of them can do so via HTC's Viveport dev portal.