I agree that stereoscopy isn't the only thing going on. But are you saying there are VR headsets that don't have stereoscopic 3D, and that I should therefore change my analysis?
I don't think spatial experiences are particularly new.
Quake was the first game I recall playing that was intensely spatial. So much so that after a couple of hours playing I had trouble readjusting to meatspace; the positional part of my brain was still carrying enough of the virtual world that i was easily disoriented. The same thing happened to me with Minecraft. Years later, I still have vivid spatial recall of some of the bases and mines I built.
You could certainly argue that VR controllers are an exciting step forward in spatial interaction. But things like the Wii and the Switch's (less capable) motion control mean they're only a step forward, not a leap. And that also makes clear that motion control and VR are separable concepts. I look forward to seeing the fancier controllers migrate to other platforms to see how that goes.
So I think what makes facehugger VR unique is stereoscopy. And stereoscopic 3D is a thing with a long history of faddish excitement followed by a total crash. You could argue that's not relevant here, but an awful lot of VR advocates make their cases in terms of 3D.
