If Disney can successfully acquire Fox's film and television assets, this will be good news for Marvel fans. The deal will bring the rights to the X-Men movie to Marvel Studios and open the door for these characters to join the Marvel Cinematic Universe.
While Marvel Studios president Kevin Fiji has been vague about the X-Men series, in his words, is still waiting for a confirmation call. But the MCU's latest Ant-Man and Wasp May have laid the groundwork for the introduction of the X-Men.
In Ant-Man and the Hornet, Hank Pym and Hope Van Dane (second generation Hornet) realize that Janet Van Daene (the original Hornet) may still be alive despite being trapped in the quantum realm. This suspicion was confirmed when Scott Lang (Ant-Man) received a message from Janet from the quantum realm. Although there are still ghosts in the middle of this, they still succeed in rescuing Janet.
Without the influence of the later Avengers: Infinity War, it would have been a perfect ending. The key issue is not that Janet was saved, but the impact of the quantum realm on her. Because she has lived in the quantum realm for so long, she has become different from before. The quantum realm is changing people in every possible way, as Janet told Hank: "Adaptation is part of it, but more is evolution."
This "evolution" has given Janet a number of other new abilities, including quantum telepathy, the ability to use her quantum energy to stabilize others, and possibly even more. This opens the door to explaining the various forces in the X-Men.
Marvel Studios is known not to use the term "mutants" when describing characters' superpowers. That's why Crimson Witch and Quicksilver were explicitly set in Avengers: Age of Ultron to have their power coming from psychic gems rather than mutants. The MCU also bypassed the term mutants by using "Inhumans," although the TV series Inhumans had been canceled.
Janet evolved without any other intervention by being exposed to quantum energy, and Marvel may also use the quantum realm to unlock the abilities of other characters. However, not everyone who comes into contact with the quantum realm automatically acquires superpowers, like Hank Pym and Ant-Man, who have both been to the quantum realm but have not acquired any other superpowers.
With the Quantum Realm as a potential source of superpowers, Marvel will be able to build its own X-Men without having to stick to the previous settings, or either the X-Men or any other character with mutant superpowers. Whatever Marvel's next step is, the quantum realm will offer Marvel a lot to explore.