The X-Men are finally coming home.

No, not home to the X-Mansion, but to Marvel Studios, the movie-making arm of the comic book juggernaut that created these characters in the first place. Disney’s $71.3 billion acquisition of 20th Century Fox means, among other things, that Marvel will now own the rights to the characters from the X-Men, as well as the Fantastic Four series — rights Marvel sold in the late ’90s to avoid bankruptcy.

For fans of the superheroes, the X-Men and Fantastic Four new home under Marvel’s cinematic supervision likely sounds great, considering how well Marvel makes movies — and how extremely bad some of the X-Men and Fantastic Four films have been. (X-Men: The Last Stand, Wolverine Origins, and the 2015’s Fantastic Four are the unholy trinity of bad Fox’s bad Marvel superhero flicks, if you’re keeping track.)

But while the merger seems like a better home for the X-Men and Fantastic Four, and perhaps some better movies on the horizon, there are still some big problems — time, continuity, and fitting these characters into Marvel’s cinematic formula— that Marvel will have to deal with.

The timelines don’t exactly add up, especially for Magneto

The Marvel Cinematic Universe doesn’t have a hard set of rules that it abides by. Scarlet Witch’s powers have changed since her first cinematic appearance, when she had some kind of psychic mind control stuff in Avengers: Age of Ultron. The limits of Thor’s survivability are unknown, as we last saw him drifting in space in Infinity War. And there’s not much explanation for the “jumps” that connect the Guardians of the Galaxy to places like Xandar, Ego, and Sakaar.

But the MCU does make a concerted effort to stick to its established timeline.

Events that happened in the 1940s-set Captain America: First Avenger, including Steve Rogers’s conflict of being a man from a different time, Red Skull’s disappearance, the power of and Howard Stark’s research into the Tesseract, have come back to factor in future movies like Captain Marvel, which is set in 1995. And events in Captain Marvel, like Carol Danvers meeting Nick Fury and then going off into space, led to the Avengers Initiative, which is set into motion in other MCU movies, taking place years later, in the present day.

This adherence to chronology would make it difficult to incorporate the X-Men characters. Mutants’ existence within the MCU would bring new continuity questions: How did they operate without SHIELD noticing all these years? Further, what were mutants doing during the major Marvel events, like the Chitauri invasion, Ultron’s assault on Sokovia, and Thanos’s snap? Marvel could write around that, but it would have to ostensibly create chronological alibis for each of the characters.

But the major difficulty is when a character’s origin story and real history are intertwined — as is the case with Magneto.

Magneto, in the comics and now multiple movies, lived through the Holocaust as a young, Jewish boy, and the loss he experienced shapes his worldview. If the MCU wanted to keep Magneto’s origin story in line with its current chronology, it would then mean Magneto would be an old man in the current MCU; while the same is true for Captain America and Bucky, they are only still alive are because of government experiments. Their peers are either very old or have already died. (Peggy Carter dies in Captain America: Civil War, which takes place in/around 2016.)

The latest X-Men movie, 2016’s X-Men: Apocalypse takes place in the ’80s and Magneto, played by Michael Fassbender, is supposed to be in his 40s, possibly in his 50s. In a movie set in 2018, he would conceivably be around 80 or 90 years old assuming he is 13 or so in the 1940s during WWII (mutants, according to the X-Men comic books, begin manifesting powers during puberty or adolescence).

Marvel Studios is left to face the dilemma of introducing a Magneto that may be too old to be a central villain or a Magneto that doesn’t possess his crucial origin story.

There are still a lot of other Marvel movies to be made

One of the most mysterious things when it comes to Marvel, besides what will happen in Endgame next month, is what its film schedule will look like following this phase of the MCU. Spider-Man: Far From Home, a joint project between Sony and Marvel, will be released in July and will be the last Marvel project to arrive in theaters this year.

Marvel hasn’t said what its schedule for 2020 releases and beyond will look like.

We do know that there’s an Eternals movie happening, as well as a Black Widow solo movie. We also know that there’s a Black Panther sequel in development, as well as a Doctor Strange follow-up; and the third Guardians of the Galaxy movie is now a go with director James Gunn back at the helm. Earlier this month, Marvel named a director, Daniel Cretton, for Shang-Chi. And you have to take into account that Captain Marvel will most likely have a sequel, considering it’s on the verge of making $1 billion at the worldwide box office.

That’s seven movies in the next few years. For good measure, throw in another unannounced team-up movie or two. Add to that the reported TV project featuring Vision and Scarlet Witch, and a different series featuring Falcon and Bucky, and Marvel still has a lot on its plate.

That’s a jam-packed schedule. And if the X-Men and Fantastic Four are incorporated, they will have to be folded into the universe in a way that doesn’t disrupt the current story that Marvel wants to tell in the upcoming Phase 4.

Another thing to keep in mind is reports that Deadpool will be the only property to continue in its Fox-owned form post-merger, signaling that Fox’s X-Men: Dark Phoenix, which is set for June, and New Mutants, tentatively scheduled for August (reports say that New Mutants might me be pulled if it doesn’t impress Disney execs) will be the last go for the franchise’s current cast. If that is the case, and especially depending on how Dark Phoenix is received, Marvel might see fit to wait a few years before resetting and rebooting the X-Men franchise.

The more plausible scenario is Marvel using villains from former Fox-owned properties, like Galactus and Doctor Doom, in an upcoming movie sooner than the beloved superheroes themselves.

Marvel movies are great, but they’re not all that different

The initial division of Marvel character film rights made Marvel Studios better creatively. Fox’s ownership of some of the biggest series in the comic canon forced Marvel Studios to take a lesser-known hero like Iron Man and build a universe around him.

Throughout the ’80s and ’90s, the X-Men, Spider-Man, and, to some extent, the Fantastic Four were the faces of Marvel comics — hence the reason why Marvel sold the film rights of these heroes to movie studios back when it didn’t have one itself.

Because Marvel didn’t have the rights to Spider-Man or the X-Men once it entered Hollywood, it had to think outside of the box about which characters to promote on film. In Iron Man, the studio found a different hero (sardonic, tech-savvy, arrogant, damaged, etc.) than ones we were used to seeing.

It also led to the strategy of interlocking films. Marvel pitched a bigger picture of myriad superheroes who, by themselves, did not have the same kind of fervent audience interest the X-Men did, combining to form a superhero team. And it resulted in success: Marvel’s first team-up movie, The Avengers, made more than $1.5 billion for the studio.

However, that strategy resulted in Marvel movies seeming more concerned with setting the table for future installments (see: Marvel seeding its films with Infinity Stones in the lead-up to Infinity War) than telling evocative and ambitious stories. The result is locking its movies into a holding pattern.

A recent example is Captain Marvel, which was deliberately set in the ’90s as to not disrupt the current story at hand. Even then, it’s hard to picture a Marvel movie that doesn’t feel connected in one way or another to the others.

The formerly Fox-owned heroes aren’t locked into that system, nor have they starred in anything like it. X-Men: First Class’s stylish Cold War superhero team-up movie is nothing like X-Men: Days of Future Past’s dystopian time-travel adventure. Deadpool is a raunchy comedy full of butts, murder, and jokes about chimichangas, while 2017’s apocalyptic Logan is a bloody Western that received rave reviews.

Tonally, there’s no mistaking Deadpool for Logan or any other X-Men film. There’s no interchanging the Logan (a.k.a. Wolverine) in Logan with the Logan from the X-Men movies. And there’s such a stark difference between Days of Future Past and First Class, a difference that’s hard to find when you compare two Marvel movies (e.g. Thor Ragnarok and Black Panther, though seemingly disparate in terms of style and setting, contain many of the same beats and themes — fathers’ secrets, loyalty to a land, outsiders threatening that land).

To be clear, that freedom has resulted in some clunkers, like 2009’s X-Men Origins: Wolverine and the completely dismal 2015 Fantastic Four remake.

But it’s also resulted in superhero films that take risks, delve into different genres, and play around with different modes of storytelling. The results haven’t been consistent, but breakout movies like Logan and Deadpool are proof that risks can pay off — and it’d be a shame if Marvel regaining control of the X-Men and Fantastic Four on film means those risks aren’t taken.