> Mutter is a window manager initially designed and implemented for the X Window System, but then evolved to be a display server ("Wayland compositor"). It became the default window manager in GNOME 3,
Gnome alienated some developers around the time of GTK 3, and there have sometimes been regressions, and some opinionated unconventional design choices that everyone else was stuck with. (At the same time there was much positive benefits from the efforts.)
Even though I don't use the default Gnome desktop on most of my systems (I usually prefer XMonad or i3wm atop X11), I still end up using applications programs written to GTK and Gnome libraries.
Maybe this even harder push by Gnome on Wayland will drive even more effort into the alternative software, and continue to fuel the healthy competition that (for better or worst) the Linux desktop is stuck with.