I just switched to a 4K monitor for my Ubuntu desktop system. Everything was automatically recognized. I just had to use one of the settings to scale things up to my liking.

Beyond this, a couple apps were still of the wrong font scaling so I had to tweak them individually. Lastly the console and boot fonts have to be changed separately but there was an online link that gave me the command line settings to make those happen. In the end the effort was not not much more than I dealt with in Windows.

Unity hands scaling well, but many applications just don't work well with HiDPI. But same problem happens with Windows 10. In this regard, OS X does the job better.