At the moment 4k is useless besides for PC gaming and even here its still does not make sense because of the power you need to get good FPS. (it is good for Photoshop etc tho)
There is simply nothing to watch in 4k. Old movies also have no information to fill a 4k movie file/disk because noone thought that we would ever need something like that.
So there is no chance to ever see Back to the Future, StarWars EP4-6 or Indiana Jones etc in 4k. Even 2000s movies often lack 4k source material. Then you have movies with CGI that was rendered in 1080p so when a movie will be in 4k the 3d effects will still be 1080p (because studios are dumb sometimes. They would need to remake those effects etc)
We also need movies with less motion blur and displays that generate less motion blur while showing the movies more than we need a higher resolution for movies. Movement resolution is often not even half the resolution of still images.
I dont know a single TV that offers 1080 when it shows normal moving images. Its only for static images or really slow slow-mo stuff. Thats why there is always slow-mo and stills shown in shops etc.
And mobile actually does not need more than 1080p I mean my 7" tablet is 720p my 50" TV is 1080p the image of my 7" tablet is 14x sharper than my TV's image that is more than enough.
So the only people that need 1080p+ are people that need alot of "space" on their screen for photoshop etc.
