so to finally comment here:
Sooner or later VR headsets will introduce the concept of foveated rendering rather than 8k-- think a 1080p display just for the center part of your eye, which tracks your eye saccades, then a second 1080p display for the periphery. Why? For all the reasons above-- I've seen estimates on pixel handling for VR and it goes to 8k*2 or more if you want to retain angular resolution.
Now for desktop displays I can see 8k, but not for images: high res helps text or lines. on a 30" display this allows for very precise letter spacing/kerning and nuanced typography
