I have 4K monitor on laptop and also as external monitor but I have no problem with linux (using debian testing with gnome 3). I can easily combine it with 1080p monitors. Everything works out of the box.

I still switched to 1440p as 4K is just better looking 1080p. You cannot fit more information on the screen with scaling and without scaling everything is too small. I work as backend developer so space is more important for me than visual quality.