Does such resolution even make sense on 15.6" screen? You won't see any pixel difference with a lower resolution most likely (unless you look at the screen from a very close range).
Actually it does. It essentially looks like print including things like readable 4pt fonts. Now do you want to burn your battery on the GPU that is needed to drive that thing at full speed? That is an interesting question. Does the lack of a backlight compensate? If I were a betting person I would guess this is the display of the new Macbook Pro.
I owe a Dell XPS 13 with 4k display running Linux. Fonts are clearly much more sharper (maybe even feel darker) and pleasant to read than 1080p or even 2k . Although, I see you point. For most practical purposes it does not make difference I think, but I really love 4k when I'm programming. These days I'm not programming much, hence switched to 1080p as little experiment (and got fed up with sloppy GNOME performance), and I would say I don't notice much for general tasks.
Yes. 2x worked perfect for me at 4k, and its the default for hidpi settings I think. When I switched to 1080p I had to manually increase font sizes (not overall scaling) because the default size wasnt sharp/readable enough. Its pretty cool 4k now works so well out-of-box on Linux. It was nightmare in 2015.
