As we had/have the same (sort of) accepted standards:
720p
1080i
1080p
4K
8K
The latter two being used in "The Industry" before they find their way eventually to consumers.
Can anyone remind me why Apple decided to come out with something totally non standard in 5K, which I'm guessing will just turn into a white elephant device.
Apart from the fact of course than someone was able to build the panel and Apple fitted their panel just for the sake of it.
I think there were two reasons.
1. If you edit 4k video, you can view it pixel-for-pxiel and have your tools visible on the screen.
2. It allowed Apple to say they had the highest resolution in the industry.
I find my iMac 5k totally awesome and I can't see any benefit from going beyond that. I was foaming at the mouth to get a retina iMac, but 8k for me would be the same thing as offering 16 processors. I don't do anything that could take advantage of it.