Frequently within our forums and elsewhere the X.Org 7.8 Wiki page is cited, since it mentions "XWayland integration" as one of the prominent features. While it's a goal of the X.Org/Wayland developers to mainline this support, and for X.Org developers to deliver on the proposed features, it isn't a commitment to deliver them in the next release.
X.Org "katamari" releases have become rare and less important in the modular world and where distributions are quick to pick up compatible package updates. In terms of the X.Org Server features -- like integrating the XWayland support -- that's up to the xorg-server component release schedule and development work. The X.Org katamari releases just bundle in all of the packages together at one state.
As I wrote in June of 2012, X.Org 7.8 will not come for a while. Additional reasons are explained within that article.
Oracle's Alan Coopersmith confirmed as well this weekend in the forums about not to put too much weight into that Wiki page. Alan noted, "many of those todo list items just get copied forward from release to release since they haven't been finished yet, and no one is actively working on making a X11R7.8 release plan. (Maybe we'll discuss one at XDC, if we can find someone to be release manager there.)"
So at next month's XDC2013 developer event they may discuss doing X.Org 7.8, but that's not to say XWayland will be part of the release. X.Org Server 1.15 is what's actively under development but will likely be released in the next month or two. It's unlikely to see XWayland integrated into that server release so it may not even be until early 2014 before seeing the needed support from the mainline code. XMir support also really isn't a target as Canonical is just patching their X/Mesa packages for Mir.