The absolute favorite part of Comic-Con is seeing like a Mass Effect guy hanging out with a Sailor Moon, and they're just having a great time. Nerds, we love what we love with a passion and sometimes it's an angry passion, and to see that all sort of bleed out and everybody just connect.
Whatever we do would likely happen before or during the events of Mass Effect 3, not after
The whole idea of Mass Effect3 is resolving all of the biggest questions, about the Protheons and the Reapers, and being in the driver's seat to end the galaxy and all of these big plot lines, to decide what civilizations are going to live or die: All of these things are answered in Mass Effect 3.
Mass Effect 3 is all about answering all the biggest questions in the lore, learning about the mysteries and the Protheans and the Reapers, being able to decide for yourself how all of these things come to an end.
For people who are invested in these characters and the back-story of the universe and everything, all of these things come to a resolution in Mass Effect 3. And they are resolved in a way that's very different based on what you would do in those situations.
or simply:
