8k will never provide any benefit whatsoever over 4k without greatly exceeding the THX and SMPTE recommended viewing angles.
https://referencehometheater.com/2013/commentary/4k-calculator/
I like this calculator because it allows you to adjust for better than 20/20 vision. If you wear glasses like I do, chances are you may have better than 20/20. Last I tested I had about 20/12 vision. According to this calculator, I'm just at the point 4k becomes visible on a 55" screen seated 9.4' away, and this can be confirmed by the fact I notice an increase in detail between 2k and 4k content (even without hdr).
At a 66" screen, I get the full benefit of 4k. At 70", I reach the maximum viewing angle for cinema (40 degrees). At that point, I still wouldn't be able to resolve the pixels at 4k.
8k would be nothing more than a marketing gimmick.
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