It looks like it will be an adaption of the storyline from The Uncanny X-Men issues 141 and 142 in which a young Kitty Pryde is contacted by her future self to stop an act that would start a war between Mutants and humans resulting in concentration camps and nuclear holocaust. It seems like a tough plot for a movie, but I generally trust Bryan Singer who directed The Usual Suspects and X-Men First Class among others.
The most interesting part of the movie is the huge ensemble cast. This movie is suppose to be a sequel to both X-Men Last Stand and X-Men First Class, as well as The Wolverine movies. Expect to see pretty much everyone that has been in an X-Men movie show up at least once… Including Halle Berry, Hugh Jackman, James McAvoy, Patrick Stewart, Jennifer Lawrence, Sir Ian McKellen, Michael Fassbender, Ellen Page, and Anna Paquin; in addition to new comer to the series Peter Dinklage.
Below is a link to the comics the story is based off of.