With the XCU expanded by both Legion and The Gifted, and New Mutants set to take it even further, I'm interested in which characters you would introduce, and who you would have play them.
However to stop this from turning to a gripe fest over Fox's existing casting decisions, there's going to be RULES:
1) You must specify which universe the character will be appearing in. Those universes are:
a) Bad Future (Origins, Original Trilogy, The Wolverine, Days of Future Past Dark Future)
b) Good Future (First Class, Days of Future Past 1970s and Bright Future, Apocalypse, Dark Phoenix, New Mutants, Deadpool/X-Force, Gambit, Logan)
c) The Gifted
Note: Because of the ambiguity of the showrunners, Legion can be considered part of any of these three universes (and frankly, given the nature of David's powers, he very well COULD be part of all three). I'm also counting First Class as part of the Good Future ONLY, in order to minimize resulting continuity problems.
2) NO RECASTING CHARACTERS WHO ALREADY EXIST IN THE SAME UNIVERSE. Yes, we know, Fox's casting decisions are divisive, and it's caused all sorts of arguments on the forums. Therefore, if a character already exists within a given setting, you CANNOT recast them. IE, Hugh Jackman is Wolverine in the Bad and Good Futures. PERIOD. However, some caveats:
a) If you can think of a DAMN GOOD in-story justification for it, such as the character's powers, in which case you must spell out how it will work. Mystique being recast because she takes a different shape is perfectly acceptable. A telepath like Emma in the Good Future appearing as a different actress because she's using her telepathy to make others see her as someone else is fine, so long as it's understood that January Jones is STILL her "primary" actress, and would be appearing instead whenever Emma's telepathy isn't working. Plastic surgery, impostors, refugees from another universe, and other such cheese ARE NOT ALLOWED.
b) You CAN cast a different actor if the time period allows; IE casting a younger actor to play Donald Pierce during a pre-2029 period of the Good Future, such as if you want to show 18 year-old Donald losing his hand in combat while fighting Wade Wilson in Jacksonville.
c) If a character has appeared in one universe, but not in another, you can cast a new actor in the universe in which they have yet to appear. IE, Siren appeared in the Bad Future timeline, but has yet to appear in the Good Future. Therefore, Siren can be recast in the Good Future.
d) Characters who appeared in the "Bright Future" coda when Logan awoke in 2023 (specifically, Rogue, Iceman, and Kitty) but have yet to appear in any other part of the timeline may be recast (thus Cyclops, Jean, Storm, and Colossus are unavailable in the Good Future).
3) Try to give us a reason why you think they'd be right for the part, not just a name and a picture.
4) Officially Announced castings for films yet to be released are to be considered as definitive as films already released (sorry Gambit fans, until he leaves the project Tatum is still "it"). However RUMORED castings that have not been acknowledged are free game until officially announced (so Lilandra and Dazzler are both currently free).
5) NO REBOOTS. The available universes are what they are. Work within them.
So, a couple to get us started:
Selene Gallio - Good Future
Eva Green.
First of all, I absolutely LOVE Eva. She's absurdly beautiful, and excels at playing dark, powerful, manipulative, and dangerous women. All of which perfectly describes the Black Queen. As a bonus, she's a bit of a geek with a love of the macabre and paranormal, and Selene's background as a mutant vampire with aspirations of divinity would be a role right up her alley.
X-23 - The Gifted
India Eisley
Dafne Keen was wonderful in Logan, and I can't wait to see what's in store for her next in films (seriously, Fox, just announce the movie already!). However the separate universe presented by The Gifted also offers an opportunity to take a different approach on the character, one that heels a little closer to her depiction in the comics.
I've mentioned this one before, and it's India Eisley. Not only is Eisley just about a spot-on physical match (pretty and of unassumingly small build, with pale skin, black hair, and green eyes) but several of her past roles — particularly Eve of the Underworld series, and her role in Kite — pretty much ARE Laura Kinney. I could absolutely see a spin on NYX as her introduction in the Gifted, with Eisley in the role.