All the money seems to be on Sadie Sink’s role in Spider-Man: Brand New Day being the introduction of Jean Grey into the MCU, and the rest of the X-Men will then follow. So, as a result, the internet is a veritable wild west of casting speculation.
There is another rewrite underway, as revealed by director Jake Schreier. Lee Sung Jin and Joanna Calo are currently at work on that. This would mean that casting cannot begin in earnest, as lots can change in a rewrite. A high number of rewrites is a normal practice for big studio movies.
Despite potential changes lurking in a rewrite, Jeff Sneider at The Hot Mic still claims that several actors are under consideration for upcoming roles.

First up is Marty Supreme actress Odessa A’zion as Rogue. Also in the same report is A Knight of the Seven Kingdoms star Peter Claffey as Beast. Sneider has a decent hit rate when it comes to the MCU.

One interesting addition to this story is an interview with co-writer Sung Jin in Variety, where he said:
“I love Gambit. I also love a lot of the side characters. I love Jubilee. Everyone goes for Cyclops and Wolverine, but for me growing up, I always loved the supporting members.”
Other news here is that Sneider now thinks there are some release chnages coming up, and the rewrite means that X-Men will not go straight into production after Avengers: Secret Wars wraps.
Marvel always puts placeholders into schedules, and they have May 5th, July 28th, and December 15th reserved in 2028, with X-Men previously widely tipped for May. Sneider says that another Deadpool movie is now likely to take that date with X-Men going later in 2028.