Casey Hudson, executive producer at BioWare, explains that the game will ship with a number of "kits," which define what species you are and how you play. "You can unlock different characters that allow you to be different species, races, and have very different kind of movement abilities, different powers."
So far, BioWare has shown off the Krogan, Asari, Drell, Salarian, and Turian races for multiplayer. (As well as "humans.") But, what if a fan-favorite race doesn't make it into the game? (Who doesn't want to fight as an Elcor, right?) "We're going to be shipping with a pretty impressive array of different things you can unlock... but we're also planning on expanding that over time," he added. That sounds like DLC to us.
While refusing to elaborate on specifics, he did say that "anything is possible."
Mass Effect 3 will be available on March 6th, 2012. For an early look at the game, a downloadable demo will be made available in January. Access to the demo is granted via Battlefield 3 and other, as-of-yet-unannounced means.