I sincerely doubt that I'll go for 8K....watching the BBC's "Planet Earth II" in 4K is already a metaphysical experience for me.And I just bought Lawrence of Arabia in 4K but haven't watched it.Possibly this weekend.
If you're curious and have some free time you can see my 4K collection at "bluray.com" under screen name "listerone".
Also, if you have Cable, Satellite, or Streaming, 4k displays can make new and old movies or series look like they were just made due to the great up-scaling. I haven't noticed and much difference between bluray up-scaling and older discs on my 4k displays. However, bluray gives a more spacious sound.
I doubt I will also go 8k until an affordable projector for my 110" screen. THAT would be a true theater experience. I'll look into 4k projectors and that might be enough for now if I can afford one. Bottom line, the contrast on 4k TV's is amazing. You can actually get true black while seeing every star in the sky. True black is what I've always wanted. Now I have it with the correct contrast and brightness adjustments. That is the trick to 4k - adjustments for your ambient light situation.