Maisie Williams has been cast as Rahne Sinclair for the New Mutants film, while Anya Taylor-Joy will be Illyana Rasputin. This went around at least once before as a rumor. It’s being officially confirmed this time.
While I have no interest whatsoever in Game of Thrones, I have seen Maisie Williams in Doctor Who. She can act. However, I’m not entirely sure how good of a fit she would be for Rahne. I have seen Anya Taylor-Joy in Split (2016); from all I've read, she's far better as Thomasin in The Witch (2015). I have yet to see it, so I wouldn't know.
In order to make any sort of sense, they’ll probably have to scrap Illyana’s origin story of Limbo and Belasco. Then again, Warlock is supposed to be in the film, too. Karma is being left out. It would have been nice to see her in a New Mutants film.
I don’t know what current actress could work as Dani Moonstar.