5. Or Mystique Could Die...
Singer and the production team have been quick to ensure that fans are aware that their version of Days Of Future won't necessarily be a straight adaptation - to do so would rob the director of the power of the twist, and of expectation, and Singer probably isn't keen on giving up that much control over his audience. That could mean that the normal events of Age Of Apocalypse's start aren't set out the same way, and that though Magneto turns his back on his anti-human agenda - and consequently on the assassination attempt on whoever replaces Senator Kelly as the target for Magneto's plan in Days... (could that be Nixon?) - it isn't necessarily Xavier who dies to change his opinion. The trailer for Days Of Future Past included a very obvious fight scene between Magneto and Mystique (where we see her being dragged along the floor towards him as above,) and it could be that Singer has reimagined Magneto's trigger as his being forced to kill Mystique when she turns on him to stop his plot to take out his target. The way Magneto feels about Mystique - and particularly his insistence that she be true to her purer mutant form - could well lead to a stark realisation that he has to change his stance on mutant-human coexistence when she dies. Regardless of how it happens, the change in Magneto is what inspires Apocalypse to attack the Earth to advance his own agenda of mutant control.