It should be easy to create something better than X11. And if not pour more resources into X11 developement. Wayland on the other hand is a complete failure on all fronts. It should be abandoned ASAP.
It has worse performance on almost all metrics. Heavy fragmentation. Very limited and incomplete API measured in functionality but still extremely complicated to work with as developer. Extremely slow development. The only thing that it has over X11 is better funding (for whatever reason).
Mixed DPI works perfectly fine on X11 if the toolkit supports it. The xrandr protocol provides all the necessary dpi information. GNOME simply chose not to support it on X11.
Reading some of this thread has made me feel like I'm going insane. I have a wildly different experience of both X and Wayland from a lot of people in this thread it seems.