Unfortunately many people think that VR didn't exist before Oculus Rift. Which is, of course, BS. There was good quality VR available before as well but unless you have worked for a large university, the military, NASA or some large aerospace/car company, you were unlikely to encounter it due to the costs of the equipment involved. Industry-grade HMDs still cost $15000, they used to start at $40k but I guess after the cheap Oculus became available, that price point became untenable. `CAVEs and large projection setups that are commonly used for both research and training work can cost millions.
The worse part is that also quite a few people from these companies - Oculus, Valve and others that are jumping on the VR bandwagon now - tend to ignore the decades of existing research. Most people there are businessmen and (briliant) engineers, not researchers (with a few exceptions). They tend to massively reinvent the wheel and to rediscover things known for many years, because they don't know where to look for them. If they didn't, they would know that increasing framerate and decreasing input latencies is not going to fix the motion sickness. Sure, laggy, smeared image in the HMD will make people sick. However, you can and will get sick even at 120fps - it depends much more on what you are rendering than at how you are rendering it. A virtual rollercoaster will make people throw up even at 4k resolution rendered at 250fps with perfect head tracking. It would look awesome, though ...
The problem is mainly the content, not the technology - the content must work with the technology idiosyncrasies (I won't call them limitations - that implies they could be overcome, but sometimes it would require changing the laws of physics or it would cost so much that it just isn't practical), not ignore the specificities of the medium ("let's play COD with an Oculus Rift, that will be awesome!" *BARF*) or expect that the "technology will improve" and motion sickness won't be an issue, no matter what wild camera gyrations, cool fly-throughs and slow motion cut scenes the game designer has put in. It is the same thing as the film directors having to learn how to shoot in 3D - the "film language" (how you convey your message through camera work, lighting, etc) changes quite significantly when you are in 3D and not every film director was/is comfortable with going there. Even the visually stunning Avatar had some issues with stereoscopy here and there. That is why the worst 3D movies were the ones converted from the regular 2D, where the media specificities were ignored.
This is very much where we are still at the begining - virtual reality as an entertainment and story telling medium. It is not a question of technology anymore, it is more about finding sensible ways to do things in VR so that the experience is fun, pleasant and something people will actually like to return to. With careful design work and working with the medium and not against it you can render even at 30fps and nobody will get sick.
In my 15 years of working with VR (involving both large projection setups and HMDs) I have never encountered anyone getting sick because of the frame rate. It was pretty much always because of poorly made content not suitable for the technology being used, poorly implemented navigation that didn't respect the specificities of the medium ("teleporting" camera, forced/constrained camera movement, head bobbing, poorly synchronized/unsynchronized treadmills ...), poor camera work/tracking ("mouselook" in FPS really is wrong for VR - you don't have head bolted rigidly to your shoulders!) and similar issues. Then you have issues like people feeling discomfort/headaches because of eye strain due to poor focus, moire, poorly set up stereo rendering, etc. It often gets incorrectly attributed to "cyber"/motion sickness, but that has nothing to do with it at all. Finally, there are people who will get sick and dizzy even from looking at a static image projected on the wall - the issues can be psychological/psychosomatic as well.
To conclude, I think it is time that we step back from chasing latencies and framerates and look at the actual underlying causes. Higher framerates and better technology in general are not the silver bullet here.