@haddock For what it's worth wayland handles mixed dpi different than X11. By some perspectives it's worse.
http://wok.oblomov.eu/tecnologia/mixed-dpi-x11/
But really despite that impressive technical writeup (it convinced me) I think the conclusion is that we want something from our display servers that neither Wayland or X11 is really able to provide.
We want mixed DPI. X11 can do mixed DPI wayland can't, we want a seamless multimonitor desktop, both X11 and wayland can do a seamless desktop but X11 loses it's ability to do mixed DPI and wayland is able to spoof mixed DPI better than X11 can(fractional scaling).
My personal opinion, I find wayland as a display server boring compared to X11 (that might be a good thing), the real interesting work in this domain is arcan. https://arcan-fe.com/about/ But arcan is one guy with a dream. I did not find it all that usable yet.