I agree with your overall sentiment with the caveat that 20 years will be closer to 5. Early adopters are enjoying Wayland only benefits today. For example, the Steam Deck just launched with HDR and mainline support for Linux gamers in general will not be far behind.
Also, the list of window managers being left behind is starting to look less appealing than the list of window managers that are Wayland only. Hyperland is probably already more popular than WindowMkaer. As GNOME and KDE go Wayland only, they will continue to add features that regular users will want. I see more announcements for new Wayland compositors than I do for new X window managers.
Another factor that gets missed is that the main dev support for X comes from Red Hat. RHEL9 is already Wayland based. When RHEL8 comes off support in 5 years, Red Hat will abandon X. How long will X stay viable after that?
As the number of X users dwindle, we will see toolkits drop support for X. GTK5 for example. 5 years may be too soon for that but I cannot see it taking 20 years.
Wayland being “valuable to most users” will come faster than you think.