BioWare has made it loud and clear Mass Effect 3's Extended Cut will not be the last piece of DLC for the title, not by a longshot.
"Would now be a good time to talk about how we're doing more DLC in the future?" Gamble wondered aloud. "That was a trick question. We'll save the future DLC for future chats. Don't worry though...there's much more,"
No specifics were provided, but it's certainly something to look forward to if you haven't quite yet had your fill of ME3.