Unreal Engine 4.21 preview is out! It natively supports Windows Mixed Reality headsets without the need of SteamVR or UWP. So yes you can make a classic Win32/64 app that works with Windows MR natively. It's great because as you may know, SteamVR is great with a Vive, but it's a real pain with some other headsets. I would love that Unity does the same implementation to exit SteamVR of our development process.