The Intel and Radeon drivers have supported server managed FDs since the start of April and it followed with the Nouveau support. The similar treatment has now been done for xf86-video-modesetting. The work comes down to the DDX drivers querying for their assigned file descriptor rather than trying to open the device directly.
Hans de Goede at Red Hat has been working on allowing the X.Org Server to run without root privileges in more hardware configurations. As part of this, sever managed file descriptors (FDs) has been one of the changes needed by the X.Org graphics drivers for supporting this change of running the xorg-server without root rights. There's also new code found in X.Org Server 1.16 and handling support done by systemd's logind.
This more secure X.Org graphics stack configuration will be found in Fedora 21 that's scheduled to ship late into the year.