Yeah I think this scene will be set much later in the game, Mass Effect has been a game about exploring the galaxy and humanity leaving our solar system, so Earth being the central location for the reaper invasion is perfect in my opinion of bringing the conflict full circle. Especially when considering what happened at the end of Mass Effect 2.
Can't wait , though I can't help but think that they need to release the trilogy as one game after this. Since if you want a clean start, or change something, you might have to play through three separate games.