According to a listing on a Sony Hong Kong website which has since been taken down, there's more Mass Effect 3 multiplayer DLC on the way, entitled "Rebellion Multiplayer Expansion." More weapons, more maps and even more characters:
The Rebellion Multiplayer Expansion opens two new fronts against the Reapers: Firebase Jade's jungle reservoir and Firebase Goddess on Thessia. In-game reinforcement packs now include three new weapons as well as equipment, consumables, and six new classes: Quarian Engineer and Infiltrator, Vorcha Soldier and Sentinel, Phoenix Adept and Vanguard. The battle continues – hold the line!