This is rubbish. Qt and GTK are not DEs, but toolkits. Further, these toolkits *both* have long supported rendering outputs *other* than X11 for a long time (from Windows GDI to direct framebuffers, even HTML). So there's just no basis to say that the addition of another rendering context, Wayland, is going to change the quality of X11 support.
The only thing that could change that is if X11 becomes so little used that no one cares to support it anymore.