A major new feature in Mass Effect 3 was recently shown at an EA press event, but won't be revealed until later this month. This news comes courtesy of Xbox World, who will premiere this "killer feature" in their next issue (October 25).
Meanwhile a flyer for Mass Effect 3 has appeared online, where it is clearly indicated that there will be an online multiplayer pass connected with the game. Perhaps something similar to Cerberus Network in Mass Effect 2, but at this point there is mounting evidence that there will be a multiplayer component in Mass Effect 3. We'll know for certain soon enough.