VR, though, is a different story. That absolutely limits the market. That being said, I'd wager that a majority of people who play VR games on PC will likely buy this game, as it's probably the first true AAA title developed specifically for VR.
I assume you're referring to the Quest? Is that a statement based on your experience playing games on it, or what you assume they'll be like?
I view it less like mobile games, and more like games put our for the Gameboy. Specifically tailored to achieve good and consistent gameplay based on the target platform. This is partially because Oculus is being very demanding in what they'll accept for their store, to the point that there's actually not a huge catalog, but each item seems to work very well.
Along the lines of the Gameboy comparison, there's been a few stories now of developers taking a game people thought couldn't make it to the Quest and optimizing enough for the platform that it performs well. There's something to be said for consistent hardware.
The price and inherent limitations (such as motion sickness) of VR are going to ensure that it doesn't hit mainstream, at least for the time being
(The price of the Index definitely doesn't make it mainstream though. Just trying to get a sense of this issue)
On the other hand, any game where your movement in the game world doesn't match the real world is a quick path to sickness. Any racing or flying game makes me ill, and I've been playing VR for over 2 years.
On modern hardware, motion sickness is only really an issue in VR games which move your head around in-game in ways which don't match how you're moving in real life. Teleport and physical movement don't cause issues for most people.
This is going to expand the market vastly because it will make it much cheaper to develop quality VR games. In a couple of years, I predict the average purchase of this game will be to play the mods rather than the core game.
Valve bought the developers and got them to create Team Fortress Classic the goldsrc engine (which started out as the Quake engine).
And let's not forget Garry's Mod either. VR physics sandbox in the HL:Alyx engine? That's going places.
Personally, being the frugal sort, I'll wait until it is on special. By which time I'll have upgraded my headset to one I can wear for more than 30 mins without it becoming an irritation.
I do wonder if the demographic is bang on the money, with a large number of headsets in the hands of people in their late 30s and 40s who remember the original Half-Life. I had originally thought Valve would first reissue the Half-Life and Portal games for VR, or even reboot Half-Life.