The theory that's flying about that I want to believe is that everything after the reaper hits you is a hallucination. It makes sense, both endings are the same anyway and once you get the perfect ending, Shepard is seen to breathe in the rubble of London.
I say wanting to believe, but that is only from a creative standpoint. If they royally fucked up that ending purely to get extra DLC bucks with DLC that changes the ending will be utter bullshit and I'll watch it on YouTube rather than pay for their shitty money grab.