High-DPI PCs have been out for a couple of years. I don't have firsthand experience, but it's my understanding that while the Windows world had to play catch-up, it's fairly decent today. Linux support for high DPI varies depending on the desktop environment (I've heard it's abysmal to mediocre).
Windows support for high DPI (4k) is absolutely terrible! I recently tried setting up an MSI Ghost GS60 4k [1] for a client. By all means it was the greatest laptop I'd ever seen, until we came head-on with Windows 8's terrible (absolutely terrible) support for 4k screens. Scaling was inconsistent and several business applications did not scale at all, rendering them unusable with no viable alternative (apart from using an external monitor).