- The Main Team -
This is the main team for the premiere film, (with the inclusion of some surprises and cameos by other semi-retired members.) I'll try not to go too deep into a potential story, but sometimes these choices make the best sense when you see the purposes they serve to the film itself. Overall, I'm imagining one X-film a year, basically all of them being team-ups in some form (potentially even with a loose Blue and Gold team distinction), even if they are branded as solo films, along with some incidental streaming miniseries to showcase characters who aren't getting a lot of screentime in films. In later movies, the idea would be to shake up the line-up pretty regularly.
Cyclops (Scott Summers) - Scott Eastwood
Scott is a tough character to get right, but a good foundation is a sort of bizarro Captain America. Someone for whom leadership doesn't come naturally, charisma is not his strength, and he only finds himself with responsibility when it is thrust on him by others or by circumstance. By this stage of his life, he has adopted a stoic facade because he thinks that's what his teammates need to see in order to follow him. But we'll get to see cracks in that once he and Corsair cross paths.
Marvel Girl (Jean Grey) - Emma Stone
For the early films, I wanted to avoid the star-power-driven impulse that has guided much of the Fox franchise so it can be much more an ensemble, but Jean in an exception. She has to connect with the audience strongly and quickly, because it's her presence and absence that will in many ways define the team. Stone has the charisma to do that out of the gate. And with her most recent comic book role being Gwen Stacy, it puts any potential Phoenix saga onto the back burner until well after this character has eclipsed the older in the viewer's minds. Jean is also purely a telekinetic at the opening of the films.
Storm (Ororo Monroe) - Kylie Bunbury
Unlike Scott and Charles, Ororo doesn't have leadership given to her by default or fiat. And when she eventually steps up to take it (something that would happen in a later film) it comes to her naturally and easily. She has the grit, brains, and heart to be the best leader the team ever has, but not the stamina to do it for long. But even though she leaves, she always comes back.
Nightcrawler (Kurt Wagner) - Matthew Beard
Sensitive, soulful, playful, and a bit cartoonish, Kurt gets along well with all of his teammates. His favorite part of the job is the sense of rousing adventures, and he's most at home when traveling to other worlds and dimensions. His idealized view of himself is equal parts Errol Flynn and Captain Kirk, and when the team finally meets the Starjammers, you can only imagine his jealousy that Scott's father is a real-life space pirate.
Psylocke (Betsy Braddock) - Emilia Clarke
The newest addition to the team, Betsy is outgoing and a little overly familiar. She is the most reluctant of the X-Men to go into the field, but her ability to serve as a telepathic link between her teammates and a means of communication back to Professor X at any time make her too valuable to leave behind. Because she is not skilled in combat, she stays far away from the fight and wears a bulky protective uniform. Unfortunately, that armor doesn't save her. In one of her first missions, she's killed, releasing a wave of psychic energy with her final breath.
- Former Members -
Less important to the X-franchise itself than to the broader MCU. The Original Five of Angel, Beast, Cyclops, Iceman, and Marvel Girl did happen, but they have since dispersed, and they are used to seed the rest of the MCU with mutants to create the perception that they've been there all along on the margins.
Banshee (Sean Cassidy) - Ewan McGregor
Bounces in and out of the X-films, most importantly as the father and mentor of his daughter Theresa in a New Mutants franchise. One of the oldest of the X-Men, he and Charles are more peers than anything else.
Beast (Hank McCoy) - Toby Kebbell
Imagine being typecast as "the CG monkey guy", but here we are. Because Beast wouldn't play a major role in the X-franchise itself, but could potentially do so in the future (or in the broader MCU), it would be nice to have someone who has already gone through the mocap learning curve. Kebbell's face could still be largely done with make-up to capture the most of his performance. Also... he's actually pretty good fit anyway.
Iceman (Bobby Drake) - Logan Lerman
Bobby was the baby of the Original Five, but has struck out on his own to pursue a normal career. It's there that he encounters a whole world of weird supercriminals that have nothing to do with mutants or mutation. He and Peter Parker as classmates isn't too much of a stretch, is it?
Angel (Warren Worthington III) - Andrew Garfield
Warren has to be smug, hateable, and shallow, but then later tragic, sympathetic, and pitiable. As far as broader MCU potential, he would be a good addition to a looser Avengers team modeled after things like the (comic) New Defenders. Obviously, there's an eye on doing another stab at Apocalypse / Archangel in the future, but for right now, he's more in the Avenging Angel mode.
- The School and Students -
For the first film, the school is basically empty. It's not a massive place to begin with, but most of Charles' students have grown up and moved on. Many of them only stay long enough to learn to control their powers and then return home/strike out on their own. But after the first few films, a class of New Mutants could be introduced (either as Charles' or Emma's proteges) and serve as more of a (dark) teen drama in contrast to the more Avengers-y exploits of the flagship.
Professor X (Charles Xavier) - Lance Reddick
I love Patrick Stewart, but he has given people a very twisted view of Charles Xavier. Charles isn't Grampa Picard, he's Lex Luthor without the inferiority complex. But because Stewart was so prominent in the Fox franchise, it means there's less flexibility to play with him in the MCU. So, he takes something of a back seat in the franchise, with the focus being much less on the school, and more on the X-Men as a super-team (which is what this series should really be anyway).
As far as casting goes, my only reluctance in picking Reddick is that it closes the door to him playing Martian Manhunter, which would be my preference. If DC had their act together enough to want Reddick for that role (and not waste him), then he should go there, instead.
Shadowcat (Kitty Pryde) - Millie Bobby Brown
Ostensibly the main character of the first film, Kitty serves as our POV character to be introduced to this new world of mutants. Despite her youth, Kitty is one of the smartest and wisest characters in the franchise (so much so that when the New Mutants who are closer to her age are introduced in a later franchise, Kitty still remains with the adult X-Men). Once she gets settled into the School, the X-Men learn she's a punk, and a brat, and... usually right.
- Adversaries with Promise -
The existence of mutants is not broadly known in the MCU when the first X-film premieres. Government agencies are aware of the phenomenon of special people, but few know of any underlying genetic cause. Professor X, Magneto, the Hellfire Club, and the Canadian nationalistic version of SHIELD known as Department H are the only major groups that know what makes mutants different than a garden-variety inhuman, and they all work to keep the existence of mutancy as unknown as possible, so as to collect and control as many of the mutants as they can in secret.
Wolverine (Logan) - Jack O'Connell
This is where I need to offer a bit of context. The first film in this series (as I'm envisioning it) would pit the X-Men vs. Alpha Flight (or more accurately Department H), and Wolverine would be among them. They have successfully implanted him with a neural implant to make him the perfect savage soldier they've always wanted, so when he is unleashed against the X-Men (and kills Psylocke), our first and most lasting impression is of a feral beast. Only when Kitty phases through him, shorting out the implant, does he return to his senses and turn on his torturers.
Psylocke (Betsy Braddock) - Elodie Yung
Before you say "she's already Elektra", you're going to need to read this paragraph. When Wolverine kills her, Betsy's psychic essence gets dispersed into the astral plane, but it also lingers around Logan. In a certain literal respect, she haunts him. Whatever is going on with Elektra in Daredevil is fine. Let it. But (in a Wolverine solo film, or a post-credit, or a special streaming miniseries or whatever) Logan encounters Elektra. Because she has been dead before, she is "accessible" to Betsy in a way that no one else is. Betsy's first impulse is to get revenge, but failing to do that, she stays in control of Elektra's body. In this way, Betsy and Elektra become these two ghosts inhabiting the same body, with death clinging to them both.
(I think it's a lot more interesting than Kwannon and it provides an opportunity to weave the films together with the Netflix shows. Though if it's not your cup of tea, this same basic structure does work with Kwannon, and I guess I would suggest maybe Melissa O'Neil.)
Rogue (...Just Rogue...) - Kristen Stewart
Introduced via a post-credit where she attacks Carol Danvers, Rogue could quickly get integrated into the X-Men itself in the second or third film as a repentant "evil mutant" once Charles and his team finds her. The fact that Charles is so eager to accept morally gray students regardless of their past is actually an important theme that troubles the other X-Men and seeds the beginning of a divide between Charles and his X-Men.
White Queen (Emma Frost) - Jennifer Lawrence
Emma is first and foremost a teacher in her own right. She operates a counterpart secret mutant school of her own, and only learns of Charles' by accident (once they cross paths with the Hellfire Club). From her perspective, the only avenues available for mutants to be safe and anonymous was with a dumb occult social club that dresses in their underwear, but the more she learns about the X-Men and Xavier's school, the more she recognizes it as a potential ally.
Because of Lawrence's history with the franchise, she's obviously to be introduced a bit later, and very carefully to make clear to the audience that she's not Mystique. To that end, probably having Mystique already appear in at least a cameo beforehand, or as part of a larger "competing mutant safe haven" storyline. And as for the casting, she's like the Frank Quitely Frost brought to life. Come on.
Magneto (Erik Lensherr) - NOBODY
That's right, just put the guy on ice for a while. Charles may imply his existence in a "we don't talk anymore" way, but for the first two to five films, Magneto is building Genosha into a mutant paradise with his own followers. When he's ready to reveal himself, he will. But this allows the MCU films to be about literally anything other than the Charles/Erik frienemesis which Fox has so thoroughly driven into the dirt...
...On the other hand... If Reddick is Charles it does offer another possibility for Magneto. A way to better explore the somewhat reductionist MLK/Malcom X parallel and especially to subvert it by making Charles less of a saint. A way to make their relationship feel fresh and different from Stewart and McKellan (and the less said about McAvoy and Fassbender the better).
Since everyone is already struggling with how to modernize Magneto as he's aging out of Holocaust-survivor range (and it's been so focal to Singer's version), the MCU might try something different and in some ways more immediate. Rather than Nazis, what if instead Magneto's family was lynched in the Jim Crow South? No more beating around the bush, since you've already seen the picture. It's Denzel.
Everything I said before about putting him on ice for a few films stands. Magneto and Charles can't be the central theme of this series after it dominated (and stagnated) for so long at Fox. But I wouldn't mind seeing how big Washington could get when in full megalomaniac mode, and he's basically the master of making severe and violent characters sympathetic and compelling.
- The Franchise -
Bringing the X-Men into the MCU presents a significant number of challenges, as well as opportunities. Of course, the potential to "do it right" after Fox spent so many years with middling adaptations is there, but so is the potential to do something bigger than a series of films in a larger shared universe.
The school itself is a good starting point. With a more modest mansion as a template, Disney could (and I think should) maintain a standing set for the franchise to work in. Not only for the films, but it creates the opportunity for television or streaming series to operate in the same literal space as the films do, providing a sense of continuity that has so far been lacking across platforms.
I'm not at all eager to see the Avengers (old or new) take a backseat to the X-Men, but the X-franchise could offer a bit of "padding" to allow Feige to release between two and four films a year, while still giving the established actors and restless directors a chance to go off, do something else, and return to the MCU refreshed and enthusiastic in a year or three's time.
Well, that's my rant spent. Don't like my choices? Don't like my direction for the series? Comment below, I guess, but I'm really sensitive about it, so why are you trying to hurt my feelings? It's just a fan-cast, man...