There are a lot of theories that surround Avengers 4, which will be an even bigger thriller than what Avengers: Infinity War was. It will bring in more characters than there were in the previous one, and this will be the ending of the MCU till Now. But it will also mark the new beginning! The film is currently under reshoots, figuring out a proper ending, so perhaps with the upcoming Disney Fox merger, they could be adding a basis for the likes of X-Men and Fantastic Four to come in as well.
It is obvious that Marvel will bring in the X-Men and the Fantastic Four in their own movies at least till 2021, but they could at least lay down the means to their entry before that. According to an elaborate theory given by Redditor PhobetorWorse, mutants already exist in the MCU, and the Snap reversal which will happen in Avengers 4 will be the one to cause their emergence. He claims that after the Avengers successfully reverse the effects of the snap, there could be the possibility that the victims would be brought back into existence and transported back to their home planets.
His theory claims that Captain Marvel will be the one who would be strong enough to wield the stones and undo everything. This means everyone is added to Earth, but she doesn’t know WHERE they are from and that is why Spidey moves to the UK in Spider-Man: Far From Home. The film will end with the heroes who are retiring from the MCU sacrificing themselves just like the end of the first Guardians movies. Then they will have a place in the Soul Stone and will be given their happy endings.
But doing all this will also work to bring in the Fantastic Four and X-Men. Here’s what his theory reads:
All of this brings people that are not on Earth, back as well. Meaning the F4 are introduced as scientists exploring the negative zone and ripped back to Earth forcefully through the Negative Zone (Reed and Sue theorized that humans could have randomly been “switched” to this zone like the real-life phase change) barrier–giving them abilities.
This is seen as the ultimate insult by a former colleague of Richards’. He was also in an accident that forever changed him, and instead of praise, his human rights violations came to light and he was forever thrown into darkness. That’s right baby, Mole Man is the villain this time. He brings to light an accident that Reed had “caused” as graduate student. This revelation paints doubt over his incredible abilities and instead neglect (Doom was the injured party. SEQUEL SET UP).”
Then he continues by explaining how the X-Men could come in and fit into the MCU. He wrote:
Have the 1950/60s see the depths to which S.H.I.E.L.D (as of Winter Soldier) went to in order to create enhanced individuals. They created a dirty bomb that had no effect on those tested (think about real-life Carbon-14). It was abandoned. This was the origins of the work seen in Avengers 2 that created Scarlet Witch and Quicksilver. The difference being the bomb’s energy surged across the planet creating mutants out of developing fetuses in gestation—it unlocked a gene). Very few of these fetuses would develop abilities.
We see two familiar figures come together in college in the 1980s and use their gifts in similar ways to help others like them. The generation they were a part of had children, Millennials. These would be the modern mutants. After the snap? Another wave of energy would hit. This would cause mutant abilities to unlock in the genes to develop throughout this new generation. People in their 30s to people just hitting puberty. This new gene would be unlocked in future generations as well (meaning we can get Bishop).
You can even have one of those soldiers impacted by my aforementioned bomb be James ‘Logan’ Howlett. He was changed, and then turned into a weapon by S.H.I.E.LD. He isn’t as storied as the comics, but everything else can be adapted. Sabretooth too. Now, all of this commotion on a universal scale brings attention to Earth. This means the new Phrase 4 will deal with larger threats.”
So, this means, everything stated by Marvel Studios to this point is absolutely correct:
It will be more “space-centric.”
Captain Marvel will be the nature face of this as she has experience with these species.
The face of the MCU will change completely. With mutants, inter-dimensional threats, etc.
New Heroes will emerge and so will their franchises.”
This theory does seem to be great on point, and the entry of X-Men and Fantastic Four in the MCU is inevitable! The only matter that stays is when exactly that would happen. Let’s just hope that it does happen pretty soon!