> On Linux, Wayland supports separate monitors natively with different scalings?

It does, but you will experience higher input latency than you would if you do not scale your display or use integer scaling. Some GUI apps might also misbehave when scaled fractionally.

I'm not sure if the higher input latency will be noticeable to someone using pretty animations in GNOME/KDE but it is pretty jarring when you mostly work on a terminal.

There's also a subtle loss of quality of text and images when using fractional scaling.