4k is ridiculous for video at current frame rates
4k has 3840 pixels across the screen. Panning an image across the screen one pixel per displayed frame at 50Hz will take 77 seconds. Anything moving on the screen at a rate faster the one minute per screen width is just a blur with multiple adjacent pixels changing on every frame and all those in-between pixels may as well not be there.
It is OK for stills although at normal viewing distances few people will be able to notice the difference from 1080p, my old eyes can't, I don't generally bother going past 720p for video.
I guess TV is going through the same more pixels is better bollocks that cameras went through despite the source (and in the case of cameras lens) not being able to support those pixels.