I think VR is quite a bit different from other input paradigms in PC development.
For one, it is always going to be significantly more expensive than any other mainstream peripheral - there's just no way for it not to be. This will always be an issue for VR development and trying to get VR more popularity.
For another, it's almost a complete separation from the normal way we interact with PCs. Mice added to what a keyboard could do, once software was properly designed for it. Controllers are fast to pick up and perform specific styles of input with (fighting games, platformers, 3rd person action games mostly) and some controllers you can sorta fudge Windows stuff with. VR you have to put on the headset, boot up special program, turn on controllers, and there's a lot of stuff that just isn't there yet as far as productivity and usability goes and honestly there's no way to make two wiggle sticks as fast as a KB+M for most day to day tasks, without doing something crazy like having a button for every finger on the wands and a bunch of dynamic hotkeys but that never took off in the past when it was presented.
It's true you can just put your headset on and use a KB+M or controller and play a lot of stuff you can on a monitor, but most of the time, why would you? It's just going to be more uncomfortable and more of a hassle (because you still have to deal with VR software to get the headset displaying at all) for arguably a neutral or worse experience.
VR is a lot of fun, and offers a ton of new experiences and new ways to explore things, and even now in near infancy it's showing really great things. But, to me it feels like a console that plugs in to my PC - it is separate, and even having grown up with DOS into Windows 3.1 to Windows 95 to now I just don't see VR ever becoming the default or norm for gaming, PC or otherwise. I think adoption will increase and more and more traditional games will have tie-ins to VR but not be designed for it, and VR games will become more and more polished and impressive.
All that said, VR is hardly a gimmick, and it also isn't for everyone (much like all types of gaming or input). I think treating VR as its' own thing is the fairest way. Half-life VR exists because they wanted to make a game for VR, not because they wanted to make a Half-life game specifically. It could be good or bad (Valve's recent track record is spotty) but it's crazy to think it would exist if VR wasn't a thing.