The next patch for FFXIV, Death Unto Dawn will be released on April 13th. Detailed is yet to be released for the patch, but players can now visit the Patch 5.5 section on the FFXIV website for a list of what you can expect from the new patch.
Death Unto Dawn will bring new scenario quests, a new alliance raid, a new dungeon, a trial, and loads more. Expect the site to be updated soon with more information.