Why 8K? Perhaps VR.
VR can be bandwidth intensive. VR immersive-gaming low-end headsets are 60 fps, and high-end are 90 fps. And I've been told 120 fps is a noticeable "like butter" improvement on 90 fps. So a 8K@30 might mean 4K@120.
VR lenses piss away pixels. With a current 1440x1440/eye, you might get only a ~500 pixel circle of crisply clear pixels. So if you want screen-comparable resolution you're all set now... if that screen is a 1980's VGA IBM PC. With this wastage, 5K/eye might let you render virtual 1080p screens.
A headset providing both wide fov and this year's "high" resolution would be about 4K/eye. And I'm thinking about modding a narrow-fov drone headset (less lens blur) with two 4K panels, because I'm tired of waiting for the game-focused VR HMD market to get around to screen-comparable resolution.
"But won't 8K require an insane graphics card?" No. The old generation of VR headsets was doing brute force. Foveated rendering greatly reduces GPU load. And frankly, even without it, I've run a VR desktop (non-immersive low-fps with camera-passthrough) on a WMR HMD using a crufty old laptop's integrated graphics. GPU isn't a blocker for higher resolution HMDs.