Microsoft regularly uses Halo as a selling point for its technology (see: the original Xbox), and that's definitely true in the virtual reality era. The tech pioneer and 343 Industries have revealed that they're working on Halo mixed reality experiences. The two aren't saying anything more at this early stage, but it's safe to say these offerings will run on Windows Mixed Reality headsets whenever they're ready... and of course, Microsoft is bound to hype them to the hilt.
Between this and the move to add Windows Mixed Reality support in Steam, it's evident that Microsoft sees gaming as an important battlefront in its quest for VR market share. It's safe to say that gamers make up a large chunk of VR's early adopters, and Microsoft needs to win them over if its own approach to VR is going to lure people away from the likes of HTC and Oculus. Halo may not be as much of a system seller as it used to be, but it's a big-enough name that it might lure players who are still waiting for a must-have title before they pick up a VR headset.