Remember when fox make Wolverine the main protagonist of their first 3 x-men movie. Disney/Marvel would do the same with Wanda Maximoff. They've said her story is not over and she will be in doctor strange 2 and possibly movies and tv shows. She is alread established character, it's make easy for people(never read an x-men comic book) to be interested the x-men movie instead of characters they dont know for a movie they nothing about.
elizabeth olsen impress me, she is a good actresse i think she could carried the x-men's movie franchise as the main protagonist