> The majority of X clients that users care about are ordinary programs
This is simply not true. The only "odinary" programs according to your definition that I am running are a browser and a terminal. All other xclients I'm running go beyond that and can not work with Xwayland or XQuartz. (a quick ´grep "^[x,X]" .bash_history´ reveals xautolock, xbacklight, xbel, xcalib, xcape, xdpyinfo, xdotool, xkill, xmodmap, xrandr, xrdb, xsel, xset)