Leviathan is scheduled to be released later this summer, most possibly by the end of August or the beginning of September.
If you've played Mass Effect 2 then I'm sure you remember Aria, the self-proclaimed ruler of Omega. In ME3 she has become stranded on the Citadel after having Omega taken away from her by the Illusive Man and Cerberus and asked you to rally three of Omega's biggest Mercenary Groups under Aria's banner to one day retake her station.
Some code in the game was found that reveals Aria dialogue that hint's at a mission to retake Omega from Cerberus. However if you already played through Mass Effect 3, the you probably already knew that Bioware had plans for DLC around this story anyway.





