More than aspect ratio or physical pixels the real metric is "inches of screen space". You can put 8k in a 13" laptop but if you want to read the window title and url bar and dock you're still eating the same amount of physical real estate as if it were a 1080p laptop. You can change the aspect ratio sure but outside of desktop setups the space constraint is already in depth so all you're doing is chopping off width that wasn't a problem while keeping the same depth profile. I.e. very few are buying a 13" laptop because 15" is too wide rather than too deep.