I'm currently using Plasma Wayland on Arch with the 1080p monitor built into my laptop and an external 4K monitor right next to it at 175%, and it works flawlessly. When a window is half on one monitor and half on the other it actually looks how it's supposed to. I can drag a window back and forth between the monitors and watch it rescale itself to run at that monitor's native resolution. Some apps, you don't even see the transition. The current scale is passed through to the applications, so text looks nice and sharp.