We do think that Niantics will be officially releasing the Pokemon GO app on the Windows Store anytime soon since they seem to be having a lot of issues trying to release the app on Android and iOS worldwide but if you still want to try out the app, there is a way to do it now.
The new PoGo UWP is now available so Windows 10 Mobiles users can start catching them all. Although the app is only in its Beta state, it is still better than nothing. Here is how to do it.
You will need to create a Pokemon Trainer Club account online before you can start to use it on your Windows 10 Mobile device like the Microsoft Lumia 950 XL. Of course, there will be some issues here and there since this is not the official version but at least it is better than no being able to play it at all.
You can go here for the full instruction on how to play Pokemon Go on your Windows 10 device.