This is one of the reasons I think it's important that VR headsets remain a peripheral instead of a platform. 3D films really only exist as long as studios find it viable to film and print 3D versions of Blu-ray, but VR is accessible to any game developer out of his bedroom that wants to do something with it. I can expect there to be continued interest for years, even if it remains niche. If Valve and Facebook decide to get out, then some other hardware manufacturer can step in when VR isn't generally a secret anymore and can produce headsets at a cheaper price. It's at least a slower death than say the Wii, which has an end of life.

They're staying the course, they're just giving the option to be grandfathered in. I doubt they'll make an effort to let people know this exists.

It's also likely just an update to Windows 10 to include everything they didn't give themselves time for by the summer release, not a successor. Windows 8.1 went through a couple of these larger updates, so I imagine it'll be similar to that.