Not necessarily - pavucontrol switched to GTK4, and there are a lot of other applications that I use that are on it as well.
If XFCE stays on X11, I wouldn’t be able to run any application that updates to GTK5 (except through some hack like running Weston nested in X, which I used to do when I used Waydroid).
XFCE is still using GTK 3, why would they care what Gnome does with GTK 5? Nobody but Gnome is even using GTK 4.
Not necessarily - pavucontrol switched to GTK4, and there are a lot of other applications that I use that are on it as well. If XFCE stays on X11, I wouldn’t be able to run any application that updates to GTK5 (except through some hack like running Weston nested in X, which I used to do when I used Waydroid).