At 1:12 they show the new heroes that you can choose to play in ME4. They are HUMANS . So my theory about a post ME3 game setting gets more plausible again.
It´s either playing alongside the events of ME1-3 or after the ending of ME3. (The heroes have an N7 badge on their armor and N7 is not that old)
BTW: Yeah that is a bummer because I hoped that we could choose the race of our character like in Dragon Age 3. I wanted to play as an Asari or Krogan but it kinda makes sense because Mass Effect has always been about humans and their heroics.