It looks like Microsoft is set to roll out its own virtual realty box, called VR Kit. Similar to Google's Cardboard, the Microsoft VR Kit works by inserting the Lumia into the slot, with the display of the Lumia driving the VR unit.
The head unit was first spotted at a Microsoft website promoting an upcoming hackathon to build apps for virtual reality. Scheduled for October 17, the hackathon page mentions that all teams that come up with "successful" ideas will be handed a VR Kit for free.
It is possible that the head unit may also be given away to attendess at Microsoft's upcoming launch event next week, although it remains to be seen if it will be sold commercially.