What If... What If Xavier didn't discriminate between mutants and mutated humans?
As the world expands around him he believe that cutting his students off from humans will only help to strengthen Erik's way of thinking, which is the last thing he wants. So, shortly after Jean joins his boys, Xavier introduces himself to Reed Richards of the Fantastic Four, suggesting that perhaps they could join forces.
It quickly spirals outward, more and more "Students' and "Teachers" are collected into the school, which changes it's name in honor of the world's first mutant. "The Namor McKenzie School For Advanced Learning".
Peter Parker toyed with the idea of joining the school, but ultimately was one of the few hold outs that never became a part of it.
The School's greatest success and failure was Bruce Banner. For years they helped Bruce tame the monster within himself. Xavier tries valiantly to mend Banner's fractured psyche, but as in our universe, telepaths trying to force a broken mind together find they have sown the seeds for great distruction.
With the school's massive staff and student body, they are able to easily sweep aside many threats that would ordinarily have been great problems. With Reed Richards, Xavier, and Banner working on the case, Apocalypse is easily stopped, though the two horse men he was able to gather (War: She-Hulk, Death; Sergie Kravinoff) were mentally broken. She-Hulk, now stronger than she'd ever been, and wearing a dark olive skin, rather than her usually radiant green, must be restrained as Xavier attempts to mend her mind as well.
Krakoa was handled by the original team of X-men first, but they were captured, just like in our reality. Next the Fantastic Four arrived, along with the Silver Surfer. after Battling the island, and freeing their friends, the Surfer sent Krakoa into space using the power cosmic.
Things began to fall apart after that. with all three Summers brothers reunited, they thought it would be a wonderful time of peace, but quickly the different groups united against them began to attack in succession: Doom, the Brotherhood, Hellfire Club. To make matter's worse, they were on the Avenger's watch list. Tony believed it suspicious that they were "Amassing" meta-humans of such high levels. Tony dissolved the "Avengers", stating that their purpose was wrong. He reformed them as the "Defenders". His team line up was that of Himself, Captain America, Dr. Pym, the Wasp, U.S. Agent, and occaionally Dr. Strange. Tony never commented to Steve's remarks that the team was entirely humans and devoid of meta-humans and mutants.
Fearing the storm that was brewing as Tony started collecting more and more human heroes of great power, Dr. Strange also called together a group. Himself, Thor, the Surfer, Namor (Who found the school humorous), Moondragon, and the mutant Angel (who had grown estranged ever since his feelings for Sue Storm had grown, despite her marraige to Reed.). this group called themselves the Champions, given their generally high levels.
They were correct to prepare as it seemed all damns broke at once. Jean, Jen, and Bruce's psychic blocks all crumbled under unknown influence. Three very powerful, and very angry entities began to ravage the land. neither the School, nor the Defenders could stop these monstrosities. The Champions were able to pacify the Hulk, while the School managed to subdue Jean, but it was War-She-Hulk that was the greatest threat. Not only was she more powerful than she'd ever been, but Apocalypse metteling had granted her new telepathic powers that drew those who were blood thirsty, and dangerous to her, granted her power over the murderous, and made her able to cloud human minds with rage.
In the end, the Defenders and the School had to join forces to combine brain power and find a way to stop her. Even Magneto and Doom lent their services, and they created a weapon that would drain not only the power that Apocalypse had given her, but all of the gamma energy that gave her her original she-hulk powers. THe only problem was that the weapon had to be applied to a specific part of her spine, right where it joined her back and neck. Any where else, and all was lost. the greatest tried. The greatest failed.
The battle had ravaged half of New-York city. It wasn't until one lone hero joined the fray, a low level meta-human that had refused the school, been condemned by the Devenders, and ignored by the Champions. As he spoke to Magneto, the latest to try and restrain her long enough to apply the device, Magneto managed to explain the situation before he succumbed to his injuries.
Spider-Man took the device. there were no other heroes close enough that could do it (Quicksilver had been killed by the high evolutionary some years earlier). Peter fought She-Hulk for an hour, never hurting her once, and being pummeled badly, but as he fought her distantly, up close, and everywhere in between, he finally found his moment. He applied the device and activated it. War-She-Hulk screamed, throwing the back of her fist into Peter's face, throwing him three blocks.
War-She-Hulk's screams of rage, became screams of pain as her powers were drained, then they became screams of regret as Apocalypse's brain washing flowed out of her with his powers. Jennifer Walters wept openly in the streets, wishing she could die. Before the others could take her, she was taken by Dr. Strange to place far away.
In the end, Xavier and Stark came to an understanding. The school continued, but now with a few more students, and a two new departments: Advanced Technology and the Human Body, taught by Prof. Stark, and Applied Sorcery, taught by Prof. McNee.