Ign has an article that kind of explores the route options Fox has for the film. While I don't agree with all of it, (mainly the Cable/Wolverine one chracter stuff), they definitely got this part right amongst some others...
They deal with heroes making difficult, often impossible choices and living with the consequences. Characters like Wolverine and Psylocke struggle with the burden of taking lives and damning their own souls in hopes of guaranteeing a better future for the rest of mutantkind.
That element, above all else, is why Rick Remender’s Uncanny X-Force has emerged as one of the best X-Men sagas ever crafted. And whether or not an X-Force movie directly adapts Remender’s work, it’s that element that should form the core of the film. Beneath the action and spectacle and violence, the movie should connect with viewers on an emotional level and allow them to see the mutant struggle in a new light.