Evolution2001 :
Another platform with it's own application base.
Daydream is about 1.5 years old, so I'm not sure why you put it like that. It was first supported on the Pixel phone. This is mainly different in that it supports 6-DoF, rather than the usual 3.
Evolution2001 :
That's at least three applications platforms now: SteamVR, MS WMR, and Daydream.
You missed a few, plus HTC is establishing yet another (not related to SteamVR).
Evolution2001 :
At some point, a consortium will need to be created for developing a standard set of APIs that they all use.
First, there was OSVR, dating back before the launch of Rift and Vive.
https://en.wikipedia.org/wiki/Open_Source_Virtual_Reality
Then, Valve outed OpenVR, which one might see as somewhat self-serving, given that no competing platform, software, or hardware vendors seemed to be involved.
https://en.wikipedia.org/wiki/OpenVR
Finally, OpenXR was initiated as the first proper consortium-led effort (to my knowledge):
https://www.khronos.org/openxr
I'm not optimistic about the prospects for adoption. I foresee most of the software platform guys dragging their feet. I think it'll be driven mostly by GPU makers and big app developers. Most players seem to be involved, but probably some are just there to veto anything that would put them at a disadvantage and possibly even to bog down the whole process.
Evolution2001 :
Similar to how Microsoft/DirectX leveled the playing field with Direct3D back in 1996.
Not sure how much of a consortium that ever was/is, as MS basically owns it and calls all the shots. Also, it was predated by OpenGL, but that was originally a SGI thing, where they made IRIS GL an open standard. They established the OpenGL Architecture Review Board to maintain & expand it, in 1992 (source: wikipedia).