Given the strangeness of the X-Men and Fantastic Four movie and TV rights, it's possible that Marvel TV can start teasing the two teams even though Marvel Studios can't. Years ago, Marvel Entertainment had sold off the movie rights for the X-Men and Fantastic Four to 20th Century Fox (through producer Lauren Shuler Donner). And every movie related to either superhero team has come from that studio ever since, including the recent Deadpool movies. But that's all going to change now that The Walt Disney Company is buying out 21st Century Fox's movie and TV assets.
Following an aggressive bidding war with Comcast, Disney upped their original Fox bid from $52.4 billion to $71.3 billion in cash and stock. While the Mouse House agreed to let go of certain assets, all the movies and TV shows under 20th Century Fox (including their television arm) will now go to Disney... eventually. Since that means the X-Men and Fantastic Four will be returning to Marvel Studios, fans have wondered when the two teams will finally make their debut in the Marvel Cinematic Universe. The short answer is: not for a while. But does that mean the MCU can't at least start laying the foundation for their inevitable introduction?
Marvel Movie Rights are Complicated
Until the acquisition officially completes in 2019, neither 20th Century Fox nor Walt Disney Studios (including Marvel Studios) can make any plans, especially with each other, regarding the inclusion of the X-Men and/or Fantastic Four into the Marvel Cinematic Universe. Beyond the acquisition undergoing approval by international regulators, teasing anything regarding either superhero team (or their members) may end up violating what's colloquially referred to as the gun-jumping clause in the United States.
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It's logical that both parties in a merger or acquisition will share information with one another to begin the process of consolidating assets - in this case, the movie and TV properties and studios - but there's a line that they need to avoid crossing in order to prevent sparking antitrust issues with the U.S. Department of Justice. And so, that's one of the many reasons there aren't any current plans to incorporate the X-Men and Fantastic Four into the MCU other than the fact that Disney inevitably wants to do so - but they have to wait for now. However, the studio may have some leeway when it comes to television.
TV Rights Are Different Than Movie Rights
Although it's never been explicitly confirmed by Fox or Disney in an official capacity, it's been heavily reported, alluded to, and even presumed that Marvel still holds the TV rights to the X-Men (& Fantastic Four), which is why several mutants have appeared in animated form over the years. That's also why FOX Broadcasting and FX Networks needed to strike a deal with Marvel TV to produce their two mutant-based TV shows - The Gifted and Legion, respectively - before green-lighting either production. It makes sense given that Disney shut down Donald Glover's Deadpool animated series earlier this year, despite that show originally going to FX.
For the same reason that the video game rights to Spider-Man are held by Marvel Games - not Sony; in fact, they were never held by Sony, only Activision at one point - Fox doesn't hold the TV rights either property. Therefore, since the Marvel TV shows are technically connected to the overarching Marvel Cinematic Universe, the studio can, theoretically, start teasing the X-Men and Fantastic Four before eventually introducing them onto the big screen. The best place to do this would be Disney's new streaming service, Disney Play, which is already exhibiting greater connections to the MCU than Netflix's Marvel shows have before.