The Mass Effect 3 Extended Cut DLC might flesh out the game's ending but BioWare's not done with ME3 just yet. Hidden in the Extended Cut files is information on a new single-player DLC pack called Leviathan.
Warning: spoilers for the alleged DLC below
Fans at the BioWare Social Network pulled the script from the game. You can look at it yourself on Pastebin. The dialogue reveals a mission to save the scientist Ann Brynson from a mining facility under the control of a Reaper for a decade.
The big twist of the DLC concerns Leviathan, the Reaper overseeing the facility. Apparently he's an outcast, a traitor who once killed one of his own kind. In the course of the DLC, you can somehow recruit him for the war effort. Seems like he'd be a big boost to your War Assets.
Brynson, meanwhile, is found to be alive. She can die in the course of the DLC, though. Presumably she'll add to your total War Assets as well, though probably not as much as a freakin' Reaper.
One of the other lines in the script suggests that maybe even more DLC is planned: "You know, whenever we discover something amazing like that, I wonder what else might be out there... or even right under our noses."
BioWare hasn't officially announced Leviathan yet so it's anyone's guess when it'll arrive. Extended Cut literally just arrived so the next add-on probably won't arrive until much later in the summer.