Inside the latest Windows 10 build, we are starting to see Microsoft provide mixed reality developers with support for MR headsets, inside of Windows 10 build 15048.
The latest build provides Mixed Reality developer kit owners to check out a simulation of the demo, but not an actual mixed reality experience. It's also not available easily, as you'll need to enable "Developers Mode" on Windows 10 that will enabled the "Mixed Reality Portal" that includes the demo.
If you've got the latest Windows 10 build, you can run the simulation - but without a mixed reality headset, it's kind of useless right now. Interestingly enough, the new "Windows Mixed Reality" portal app removes any reference to HoloLens.