"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," BioWare's Casey Hudson previously said. A purported leak shows what some of those "expansions" will be.
If the image (above) is legitimate, the game will add Geth versions of the Engineer and Infiltrator, Batarian versions of the Soldier and Sentinel, and the entirely new classes Krogan Battlemaster and Asari Justicar. It's the last two that raise eyebrows, since all of the other multiplayer classes have been based on the ones found in the campaign.
Our own Garnett Lee was impressed by the multiplayer mode in his review. Some fans were concerned it was tied too stringently to success in the campaign, but BioWare has since clarified that you can attain the "best" ending without touching it. Adding more multiplayer content seems inevitable, but without official word from BioWare, this is a rumor for the time being.
Shacknews has contacted BioWare, and will update as more information becomes available.