Singer was originally supposed to follow up X2: X-Men United with a third film. His proposed story outline, according to co-writer Michael Dougherty, would have focused on the return of Jean Grey as Phoenix. She would have appeared as a primal force, one that would wipe out San Francisco upon its arrival. A force that would have sunk a freighter carrying mutants to be used as slaves, a discovery which would have sent Dark Phoenix on a mission to fight the war against humanity her way.
But unlike X-Men: The Last Stand, Emma Frost and the Hellfire Club were intended to be the primary villains alongside
Magneto and his Brotherhood, with each side manipulating Jean for their own ends. Ultimately, the X-Men would have been caught in the middle, and eventually teaming up with their enemies to stop Dark Phoenix. The movie would also have introduced Gambit to the franchise. And yes, Cyclops was not going to die like a *****, and off-screen.