The sensor stuff Sony has coming, is spectacular.
I don't think I have ever heard it suggested that fullHD matched average vision. But this is where respecting the audience comes in. It doesn't matter what we can see, or tv we have or prefer, it's what others can see, what they will legitimately prefer or will but in the future.
Now, everybody that complains they can't see the difference between 4k and fullHD, has poor eyesight, same as the person I saw that claimed that DVD resolution was good enough for theatres. The second issue, is people that sit too far away. There are a few wide feild zones around human vision. The widest is where we have I keep looking around to see things, the second we can just sit there. The inner one is your old CRT TV like scenario, and sitting up the back of the theatre. In THX home certification, the preferred screen size in between 120-200 or so inches. Most excellent size for extreme sports.
Now, most of the population will see 4k or below, and as it gets more difficult to discern 4k seems a happy medium. 8k might be 10-20% of the population who should be happy with 4k instead. So unless you are making a teenage or younger action movie, there might be little point. At 4k most everybody should be happy.
Now, the old formular was 2400 dots per inch monochrome maximum eye resolution, halve to 1200dpi for color, halve again for an emissive screen (I wonder if more for HDR) and I think for some reason or so half again. Anyway gets to around 4k for color pixels filling up your central.wife feild of vision.
Now, another issue. For large poster prints, 4k is not that much, it avertising posters, saying extreme sports. Now, another useful feature is to be able to reframe, refocus and relight an image. Very useful in sports, action. So if we use 2k as a minimum, 4k only allows two screen length, 8k four. But, if you were filming your freinds, or kids, soccer match 16k+ might be desirable (set and forget, then frame at will during playback or editing, same with car video). But, that is only fullHD framing, double or quadruple, for 4k or 8k frames (looks like the sort of tech needed for this is coming). Then sit in front of your 120 inch+ hdr rec2020 modular led TV with your freinds and watch it.
Thancam, I would be hard-pressed to tell the difference between 2k and fullHD on a phone screen too. But when I was well I could see the lines between the pixels in the best cinema screen in town (smaller than 4k) and I know somebody with better vision than that which can pick between pixels on Apple handheld screens. There are people that can see moons around Jupiter and the rings of Saturn.