According to Next Powerup Developers attending an upcoming hackathon in Russia will be able to test the headset. Those developers will have access to tools for creating games for the VR headset.
Just like Google Cardboard, Redmond's VR Kit is made of what appears to be a cardboard-like material. Of course, it does not work with Android devices just Lumia phones.
Other details are thin on the ground. We only know about it because of promotional snaps taken for the hackathon. Microsoft has not mentioned anything about it and launch plans for the headset are a mystery.
It might never happen at all, and this is just supposed to put the frighteners up Google. Not sure sticking your nose so close to a mobile phone to simulate VR is that good an idea anyway.