The upcoming Mass Effect 3 won't have anything but a single player experience for intrepid space explorers, but that doesn't mean you won't someday be able to take to the stars with your friends. During an interview with Game Informer, Mass Effect executive producer, Casey Hudson said that concept was not too far fetched, they just had to figure out how to do it right:
“A lot of people say that they want to see an MMO, I think that kind of makes sense for this universe...Part of what you’re trying to do is save the universe so you can live in it. That’s part of the promise, I think, for any great IP. It has to be a world worth saving.I think Mass Effect has that quality to it. If you get rid of the Reapers and win that, wouldn’t it be amazing to just live on the Citadel or just take ship to Omega? That makes sense.”
Hey Casey, isn't Bioware already working on an outer space based MMO? I think it was called something like Star Wars: The Old Republic. Seems like all you'd need to do to make it Mass Effect would be get rid of the lightsabers and change Wookies into Elcors and you'd have your MMORPG done.