A third display server would probably be either useless (as in it would not be adopted or development would not takeoff) or just Wayland but without the committee. As such it would only cause more fragmentation. Plus, not anyone has the skills and availability required to make a good display server, and as of now, most of the ones that do are working on Wayland.

P.s. if instead of Wayland like it were x11 like it would stop being “de-facto useless” and become “useless by definition”