User blog comment:DeadpoolN7/Future DLC/@comment-24.60.42.14-20121206123629

For the Leviathan dlc reference about the Citadel you can check this thread on BSN which contains much all the data relating to it: http://social.bioware.com/forum/1/topic/355/index/13910521/1.

There is still two placeholder locations on the galaxy map over the general locations of the Omega Nebula and the Hawking Eta. Like the third placeholder that unlocked the Crescent Nebula due to the leviathan dlc, there may be one or two dlcs that will unlock those locations.