Then why is the percentage of gamers using VR so small? The numbers may be higher for racers and flight simmers (both small, niche genres), but in the general PC gaming world, where it really matters, there are still less than 2% of users with VR headsets according to the Steam hardware survey. Mainstream? And, yes, I have tried it.
Maybe not in it's prime now, but perhaps as good as it's ever been is what was meant? As for becoming primetime, I imagine we'll see a big percentage increase in uptake when VR/AR is a viable alternative to a screen for general Windows use because at the moment any VR purchase is a significant investment over and above the compulsory screen purchase that everyone requires for a PC to function anyway. That's always going to massively limit the audience to those like some of us, wanting one for specific tasks where VR excels and willing to pay for it compared to the majority who will use a screen for gaming because they need a screen anyway so gaming with it requires no further outlay. If you could buy a headset in future though that removes the need to have a monitor, one that untethers you from the machine using wireless transmission of the signal and one that's able to work in an augmented reality mode allowing you to stay in contact with the outside world as when working with a monitor then who knows how widespread their use could become.