Isn't there already fractional scaling support for wayland? I'm using sway and always used "MOZ_WAYLAND_ENABLE=1" and firefox always ran under native wayland without blur (like on XWayland).
So depending on the user's personal tastes, their vision, their monitor's DPI and the font rendering algorithms used, the difference might range from clearly perceptible to none.
But yes, I have a keyboard shortcut that can change the scale of my entire desktop up or down in .1 increments. It's one of my favorite Linux things because macOS and Windows sure as hell can't come close to working that well with arbitrary scale factors.
I'm a huge Wayland (swaywm) fanboy myself and I'm excited about these changes but there is still more in the Wayland pipeline I'm eagerly waiting for so Linux catches up and surpasses macOS/Windows e.g. HDR (which is something Firefox has also been slower on). I think the fractional stuff is all in "about as good as one could ask the display server to do" state for Windows and Linux at this point, the rest is apps adopting it like we see here.
Instead it has dynamic type, which changes text sizes but not the rest of the UI scale.
We'll see if this fixes it.