HoloLens is cool but most of the HoloLens applications you write will be consumed on the $299 software-compatible Mixed Reality headsets that ship later this year (it's amazing how few people are paying attention to this announcement - Microsoft uses Mixed Reality as its branding but these are basically high end VR headsets with integrated tracking for a third the price of Rift and Vive devices)[0][1]

From an application developer's perspective, the only difference between HoloLens coding and Mixed Reality coding is that when constructing 3D scenes your HoloLens app should have a transparent background so the person can see their room through the viewport because that's what they're buying the expensive headset for and in Mixed Reality you should have an opaque background because it's VR not AR.

The really big thing though is that $299 is roughly what you'd otherwise pay for a pair of big monitors. Full on virtual desktop support with floating windows for these devices is being shipped to every Windows 10 machine starting this week via Windows Update with the intent being you don't need old-school monitors just work in the headset, or with your monitors, or however you want.

Windows now has (or will shortly depending on your Windows Update timing) a built-in developer mode simulator for application testing of Mixed Reality code without a physical headset. The simulator is still a little buggy and incompletely undocumented (remember to shut it off when you're not using it) but it's pretty incredible and more than enough to start building and testing applications.

[0] https://www.engadget.com/2017/04/12/acer-microsoft-vr-mixed-...

[1] https://developer.microsoft.com/en-us/windows/mixed-reality