While he offers no citation, the same Reddit tipster who absolutely nailed every detail of the Mass Effect: Rebellion Pack nearly three weeks before Sony's Hong Kong website outed it, is back at it again with information on Mass Effect 3: Earth, the upcoming multiplayer extension and, more broadly, the "Extended Cut" DLC.
Quoting derptemp6698:
The fighting is fiercest when it's your home at stake! Mass Effect 3™: Earth adds mods, gear, and new maps for Rio, Vancouver, and London. It features 3 new weapons: Piranha assault shotgun, Acolyte pistol, and Typhoon light machine gun. Six new human N7 classes are also available: Destroyer, Paladin, Demolisher, Slayer, Shadow, and Fury!
derptemp6698 also mentioned the "Extended Cut" DLC, the one that provides the clamored-for alternate ending to Mass Effect 3 (called "expanded" here), but it doesn't shed much more light than what was already known.
An expanded ending for Mass Effect 3. Additional scenes and an extended epilogue reveal the impact of Shepard's choices on the future of the galaxy.
He had no information on a release date for either pack, and noted that they are separate extensions.
I've reached out to an Electronic Arts representative for Mass Effect to get a confirm, deny or no comment. Any uttered will be updated here.
Update: An EA representative said the company doesn't comment on rumor or speculation.
Multiplayer DLC leak, round 2! (Going to believe me this time?) [Reddit, h/t OldManOnTheHill]