Bioware's greatest achievement with the Mass Effect series may be one of universe building. In a conversation I had with Casey Hudson before the release of Mass Effect 2, he insisted that the world of Mass Effect came first — before the art, before the assets, before the story. Now that we're approaching the end of the Mass Effect trilogy, Bioware is suggesting there may be room for more stories within that universe.
"[W]e've spent a lot of time building the IP and building this amazing world," said Producer Michael Gamble, in an interview with CVG. "We don't have anything to announce, and ME3 is the end of Shepard's story of course, but who knows? We may tell additional stories in the future."
I find it interesting: the investment in creating such a well thought out universe must have been huge for Bioware, and it's testament to its commitment as a studio that the team put so much time into universe building without really knowing just how much of a success the original game would be.
Interestingly enough, according to Casey Hudson, once a world is built in full detail, the stories almost write themselves. So I would not be surprised to see future games within the Mass Effect universe.