Most applications get their Wayland support from the toolkit they are written in. Qt ( KDE ) and GTK ( GNOME ) apps are going to work in any Wayland compositor.
Some applications do “desktop” related things like try to take screenshots to set global hot keys. Wayland, strictly speaking, does not allow this. This becomes the job of the “compositor” ( Window Manager ) and so, if an application wants to do those things, it has to know how to talk to the compositor.
Increasingly, the desktop environments and compositors are aligning on how to surface some of these capabilities to applications in a common way.
As somebody that first configured X back in 1991, I agree with this message.
To be fair though, with KMS, libdrm, and libinput, setting up X is 1000 times easier than it used to be. I suspect most users never even need to open Xorg.conf or even know it exists.
Ironically, all these technologies are also used by Wayland. A lot of what Wayland does not do, Xorg basically does not do either.