We follow the developers of the respective desktop environments. As such, we will only drop X11 support for a particular desktop environment when said desktop environment no longer supports it.
In the event of KDE Plasma, the KDE developers decided to split the X11 and Wayland packages up into two separate projects as of Plasma 6.4. As such, Plasma 6.5 defaults to Wayland-only, and X11 support must now be explicitly installed. But at the same time, the KDE developers have also announced that, as of Plasma 6.8, X11 will no longer be supported.
Even though I do not use GNOME, I reckon that the situation with GNOME would be somewhat similar. But Manjaro is not going to completely abandon X11 for those environments that still support and/or require it, such as Xfce.