Marvel will need a new X-Men cast if the mutant superhero team is indeed incorporated into the Marvel Cinematic Universe. The Walt Disney Company is currently in the process of acquiring 20th Century Fox - a sale that should complete in 2019, barring any injunction from federal regulators - which will give Marvel Entertainment the movie rights to both the X-Men and the Fantastic Four. That means both teams will eventually join the MCU, but not until 2021 at the earliest.
While it seems likely that the X-Men and the Fantastic Four will be rebooted at some point down the line - should the deal go through, of course - Fox is continuing to push forward with their own mutant-related films until all that happens. But once it does, Marvel will be able to take the franchise in a direction audiences haven't seen in many years - and that requires an entirely new cast for characters such as Professor X, Magneto, Jean Grey, and more. It's worth noting that we're skewing younger with this list, from the mid-20s to mid-30s for most (but not all) of the X-Men.
This Page: Professor X, Magneto, Wolverine, Storm, and Cyclops
Ralph Fiennes as Professor X
Charles Xavier is the most important character in the X-Men; the team's name is based on his name. Now that Patrick Stewart has given 17 years to the character and gone out on a high note in Logan, it's time for someone else to sit in the chair. Ralph Fiennes should be that actor. He's one of the most talented actors working today, and he's already proven that he can take on a major role in a big fandom and deliver a solid performance. After all, not only has he played M in the James Bond films but he's known amongst young adults as the actor who played Voldemort in Harry Potter. Playing Professor X would allow him to play the good guy instead of the villain this time.
Jason Isaacs as Magneto
Both Ian McKellen and Michael Fassbender have done incredible jobs playing Erik Lehnsherr in Fox's X-Men universe, but the MCU will still need its own version of the iconic mutant Magneto. The ideal person to follow in their legacies would be Jason Isaacs, who's arguably an underrated actor who has appeared in several movies and TV shows before. In this hypothetical casting, Isaacs appearing as Magneto would allow for an epic Harry Potter reunion with Fiennes, though this time giving Isaacs the upper hand on being the bad guy... sometimes. Perhaps to differentiate Fox's version with the MCU version, Marvel might use the character's original alter ego: Max Eisenhardt.
Scott Caan as Wolverine
Following up on Hugh Jackman's tenure as Wolverine isn't going to be easy, but the right actor with the right traits can potentially give a more comic accurate adaptation for fans to appreciate - and the person to do with would be Scott Caan. Caan not only possesses the much-needed traits to play Wolverine, but he's also an exceptional actor with several years of experience under his belt, which he can leverage to bring Wolverine to life in the Marvel Cinematic Universe. And while he typically appears on television, it's not like he hasn't starred in some big movies before.
Freema Agyeman as Storm
Storm has been a wild card in Fox's X-Men universe over the past few years, only appearing twice since the prequel reboot in 2011. Considering that she's a vital character in the comics, and not just to the X-Men world, an actress who can leverage her talents in multiple films is needed - and that actress should be Freema Agyeman, who's known for her roles on Sense8 and Doctor Who. Plus, being around the same age as Chadwick Boseman will allow Marvel to easily develop a relationship between T'Challa and Ororo Munroe. After all, seeing Storm in a future Black Panther movie is something comic book fans are dreaming of happening. This could be the first step to making that a reality.