In the past few years the X.Org Server release cycle has been bi-annual and the upstream developers have done a decent job in sticking to a six month release schedule planned in advance. However, announced this week at the XDC2013 developers' conference, Keith Packard expressed interest in delaying the 1.15 release until it's more exciting.
Right now in the X.Org Server 1.15 upstream code-base there isn't too much beyond just a lot of bug-fixes throughout -- most of which, at least the critical items, have already been back-ported to X.Org Server 1.14.x point releases.
Among the items that hope to make for the delayed X.Org Server 1.15 release include the Xephyr rewrite, the DRI3 Present Extensions, and XWayland.
The plan now is to re-open the merge window on X.Org Server 1.15 release, close the 1.15 merge window by the end of October, only critical bug-fixes will be allowed after the US Thanksgiving celebration at the end of November, and to ship the final release around the end of the year. The main motivation in ending the merge window around Halloween is to make the Fedora 20 release schedule.