So am I understanding this correctly in that it only applies to Xorg, and not Wayland? Ie. that Wayland has no use for an update to DRI2?
As far as I know, correct. DRI, DRI2 and DRI3(000) are X-protocol extensions. Wayland is not the X-protocol, its the Wayland (or W) Protocol. They may use parts, concepts, maybe even functions from DRI(1-3(000)) but the DRI stack was designed as an X-protocol extensions