I'll be needing an eye upgrade before 4k on a 40" screen from 10ft away makes any difference to me.
If anything my eyesight is likely to get worse as I age so really I can't see me needing anything more than 1080p in my lifetime. Still at least I'll be able to buy cheap TVs. Roll on 8k - it will make 1080p cheaper still!
For PC monitors though - yeah fill yer boots. Like most I have my monitor sat on my desk in front of my keyboard and any bump in resolution is instantly noticeable.......then there is another problem though.....forking out for a GPU able to shove that many pixels.