yad 14 is in mx test repo, at least for mx23.
In my experience, certain graphical elements in existing scripts that use yad dialogs break. in the antiX persistence scripts button icons are not visible and the former pre-canned yad OK and cancel buttons now just display "gtk-ok" and "gtk-cancel" respectively.
other scripts, like User Installed Packages, appear Ok at least at first look.
So before any migration of yad 14 into main repos (and even then IMO not before mx25), any existing scripts that utilize yad for dialogs will require updating and checking to make sure they still work with the newer libraries. That would include the persistence maintenance scripts, apt-notifier in its current state, mx-idesktool, and many smaller scripts utilized mostly by the fluxbox release.

possibly updating /usr/local/lib/antiX/antiX-common.sh will solve some of this. But all scripts utilizing yad would still need reviewed.