I think the sweat spot is 6K. Which would probably cover 98% to 99% of people rather than current 95%. And still be good enough for the 1-2% left out.

How long do you think it will take for desktop displays or VR to hit the perception PPI limits? Sounds like we still have decade or two, given current monitors aren't there yet (are they?) and GPUs struggle to pump out so many pixels, even more so as screen area has tendency to increase.