It looks as if Microsoft and developer 343 Industries are working on a VR project centred around "Halo". This can be seen in a recent job advert for a Creative Director.
The applicant is to work on a VR experience in the well-known "Halo" universe. Unfortunately, the job advert does not provide too many details about the project. For example, it is conceivable that 'Halo 6', which has not yet been announced, could have a VR mode for Windows Mixed Reality.
A standalone VR game or a smaller VR experience could also be in the works. Or an older "Halo" title, such as "Halo 5: Guardians", will be ported to virtual reality. Since in the Job application experience in the development of AAA games is asked, a larger project can generally be assumed. Incidentally, the "Halo Recruit" app is already available free of charge for Windows Mixed Reality.
Source: DualShockers