4K tv adoption is doing fine. However the percentage of people that buy a big enough 4K tv, sit close enough, or one with full HDR is still much lower.
When I hear claims about how much better 4K netflix or you tube looks, I wonder how much better that would look on a 1080p tv as well. Ofcourse the content looks much better, 7 mbps 1080p, vs 15 to 18 mbps at twice the efficient coded, almost 5 times increase in bandwidth. When I watch a blu-ray after watching Netflix it also looks awesome again, much sharper, better colors etc. And even blu-ray only uses quarter of 1080p resolution for color. But unfortunately, 4K content and HDR are locked to 4K tvs.
1080p gaming is far from maxed out too. Textures and lod still have lots of room of improvement, as well as AA solutions that do not blur the entire picture. That's all your getting rendering the same assets at 4K, better AA. It's not like last gen when 480p games already had better assets and were trying to squeeze a 16:9 picture in 4:3 frame buffers.
Sure 4K resolution has benefits, the same as super sampling. At least rendering the game at 4K should put shadows, reflections and other effects quality on par with 1080p, as they're always rendered at lower resolutions.
It will be kind of a weird situation. 30 degree fov at 4K for TV, vs 100 degree fov at 1080p for VR. If you think VR looks low res now, wait until after some 4K gaming!