- Earth-616's Cosmic Reset Button being pressed.
- 50,000 Marvel readers saying "WTF" simultaneously.
- The Internet splitting in half. Again.
I've lost count of the number of times Everything We Know has been revealed to be Wrong lately. When you do that too often, and you never establish what Everything Really Is before you move on to the next revelation, you arrive at Nothing Really Matters. You run the very real risk of retconning away everything the readers liked about the characters.
I have visions of a super-team -- let's call 'em Avengers, there are so many groups of Avengers running around that the odds favor it -- discovering that nobody in the room is who they appear to be. Wong is the Chameleon, Dr Strange is Loki, Luke Cage is Brother Voodoo, Spider-Man is actually the Space Phantom, Clint Barton is another Skrull (but had forgotten that he was a Skrull), Iron Fist is really Daredevil, Spider-Woman is the Other, Echo is Mystique, the Ninjas are all Jamie Madrox, and Wolverine is actually Willie Lumpkin gone postal.
If there's anybody left that I've forgotten to account for, they're probably one of Shield's Life Model Decoys.