There was one of their panels, where a guy said, that it could also show Shepard's last breath. If I remember right, there was a little bit of an uproar after it in the forum.
Chris Priestly said it was up for interpretation by the player, on whether Shepard survives or the breath scene was his last breath. I'm not sure if that was just a cop out or meant to spark 'speculation,' or he was just poking the fanbase with a stick. He always struck me as being slightly trollish at times in his interaction with fans.
In any case, Tully Ackland also posted this on the BSN: "You may notice that in the “Shepard lives” ending, the love interest
hesitates to place Shepard’s name on the wall, and instead looks up as though deep in thought. This is meant to suggest that the love interest
is not ready to believe Shepard is dead, and the final scene reveals they are correct. As the Normandy lifts off, there is hope that the love interest and Shepard will again be together."
So at best you have Bioware employees giving contradictory statements.
I think there's more weight however behind the argument that the scene was meant to imply that Shepard lives. If Shepard dies why would High EMS Destroy get that extra scene and not low EMS Destroy? In both Shepard would be dying in the rubble, so the extra scene for the same outcome wouldn't make any sense. Also the files associated with those scenes are named something like Shepard_Alive_Male and Shepard_Alive_Female. And then of course with EC you got an additional Memorial scene where the LI (or a stand in) doesn't pin Shepard's name to the Memorial Wall, and then gives a hopeful smile. Like with the breath scene, there would be no reason for a different version of the Memorial scene if Shepard dies in all endings. And finally in the Citadel DLC the romance dialogue with Jack seems to foreshadow Shepard being alive in the rubble following High EMS Destroy.