Also, I do think the "Killer app" for VR has already been found: education. The US Military, Airforce, and NASA has been using VR for decades for training for example, and will continue to use them. There are several startups working on adapting VR education to other high-end use cases like surgery and enterprise training as well. I think those will still be niche, but will probably make for a couple companies with longevity in the end.
There are some unexplored but interesting pieces to the VR puzzle that also haven't been either invented or put together yet: better hand tracking, better haptics, better eye tracking, better displays, and lighter headsets for example. Potentially some combination of these will result in a 'must have' application for VR. Who can say when this will happen though.