8K gaming is the ultimate gimmick. Even in the ideal conditions they set up for that demo, I'm doubtful those gamers have the ability to detect a significant improvement over 4K.
That makes it worthwhile. That's personally what I was waiting for before upgrading my 1080 GTX TI and my monitor.
I expect to reach this we will probably have to start using foverted rendering.
I was surprised over the difference 320 Hz monitors make according to them.
Think DOTA 2 or Civilization 5. They both look amazing at 4K and I bet would look noticeably better at 8K.
Especially in those two, the games assets have enough detail to allow zooming in all the way from a bird's eye view to a first person view. As you crank up the rendering resolution, there's plenty of "real" detail available in the models and textures. You could push these games to 16K and still get more quality out of them.
Does that really matter? Integer scaling isn't really a thing AFAIK, and game devs are more likely to test their HUD layouts in 4k than 5k these days.