Currently Linux uses two different window management systems, X11 and Wayland. Wayland was intended to replace X11 but that has been proven difficult to do and to this day it can't be considered feature complete, to the point that even Steam OS primarily uses X11. Since Xorg (the current implementation of X11) and Wayland are both controlled by the same development team, there has been an issue of a conflict of interest where X11 development and maintenance has been held back, which has led to the biggest contributor forking it under the name Xlibre, so that there is less bureaucratic red tape holding back major fixes and improvements.

Assuming of course that Xlibre proves itself to be stable and has a clearly defined development cycle with clearly marked stable releases, would Valve consider using it for SteamOS, and possibly supporting the project so it can have backing and oversight?