VR is going to be just as niche, if not more so for the next 5-10 years. The impracticality and system requirements for it locked a lot of gamers out, others like myself simply don't think it's comfortable enough yet.
There are certain games with a big cult following, that are absolutely made for VR headsets. Elite Dangerous, the pending Star Citizen, and basically any flight and/or driving sim.
For folks who are seriously into those sorts of games, £400-£500 on a VR headset that they set down next to their 1080p monitor would be a viable purchase. If you can max out a game with say a 970 GTX at 1080p resolution, then you can max out the same game on a VR headset with 970 GTX sli.
Whilst VR headsets may be a bit of an indulgent luxury, 4K resolution monitors are on the otherhand the definition of the consumerist rat race. Right at this moment in time, one of the most stunning, graphically demanding, and from my own experience, well optimised games around is The Witcher 3.
At 4K, with all settings on Ultra, a Titan X will get you between 17-24 frames. I guess that a Titan X Sli configuration would get you around 35-45 frames per seconds. So with £2K worth of GPU, you are already having to knock the settings down and turn off luxury special effects in order to get an optimum playing experience (60 fps v-syncd). Sure, you can compromise with settings, turn everything down to high, turn Hairworks OFF, and you might scrape around 60 fps on your 4K monitor, with your 2K worth of GPU.......
......but what about the next tranche of graphically demanding titles that push the boat out 12 months down the line? Upgrade time already? Or what about the many titles that have issues with dual GPU configurations? Just play with one GPU and suck on consolesque 30 fps gameplay? Run the game outwith the native resolution of the monitor and get a horrible 'non-native' image, thus totally defeating the purpose of the 4K monitor to begin with? Everyone knows that Ultra on 1080p at 60 fps, is a much better experience than Medium on 4K at 60 fps, and certainly much better than Ultra on 4K at 30fps.
Expense.
Headaches.
Dissatisfaction.
Followed by yet more expense.
That is 4K gaming in 2015.