X.Org Server 1.15 was supposed to have been released in September but it's been delayed to the end of the year. With the December release target, the merge window on xorg-server 1.15 will close in a few weeks time. Delaying the release was done in hopes of being able to merge XWayland, a GLX rewrite, DRI3, and other possible new features.
Two weeks ago an X.Org Server 1.15 development snapshot was released while on Friday Keith put out another snapshot. This update though isn't particularly exciting and doesn't have the DRI3 changes, the XWayland ABI changes, or any other groundbreaking code merged.
The approximate two dozen changes found in X.Org Server 188.8.131.52 can be found via Keith's release announcement. Keith also shared an update on the DRI3 extension for those interested. This update has some DRI3 Present Redirection additions and other changes.