In keeping with a roughly six-month cadence between major releases, the plan is to ship X.Org Server 1.16 final on 1 July 2014. Of course, given the past release history of X.Org Server updates, this date could sway from a few days to a few months.
If the schedule is maintained, the X.Org Server 1.16 merge window is open now through 1 April, followed by a period of bug-fixing until 3 June. In June the goal is then only fixing release-critical issues.
This quick and rough release schedule with no major surprises can be found on the xorg-devel list.
Only the release schedule was given and no hopes of features to have merged for this next major update. Many would be excited over seeing XWayland (or XMir) support. One set of patches already queued up for merging is eliminating the X.Org Server compiler warnings -- going from 1,000+ compile-time warnings at present and now down to zero. If there's any other changes you are looking forward to see with the X.Org Server, share your thoughts within our forums.