I installed elementary OS Loki 0.4.1 on a Dell XPS 9370 and for the most part of it, the support for high DPI screens is good enough for me. I only had to increase the text size to the highest available but I guess that's more of a preference. The only problem I currently have is that the dock, while switching windows (Left Alt + Tab) looks really tiny, my guess is that it's not running on the same 2X size like the rest of the UI.
Consider this screenshots, both have the width of my screen (height is cropped):
How can I fix this? It's not a huge deal but sometimes the animations between the two dock sizes are really ugly and distracting.