3. Leaving An Open Ending
This is definitely a risky one. There are many movies that have an open ending, hoping to soon have a sequel to tell the rest of the story, only to end up being a huge fail at the box office, killing any chance of the cliffhanger ever being addressed, or answers that are actually necessary ever being addressed. Not to mention that those who enjoy the movie would be very disappointed to know that they will never know the rest of the story. There are many ways they could approach something like that. From what we know based on Brian Singer's comments regarding the plot of the movie 30% of it takes place in the future, so it's highly unlikely that we'll see everything they need to show about the future X-Men. Not to mention how difficult it is for a movie to give satisfying closure to all of its characters they'll need a longer running time for the amount of characters involved in the film. When done properly an open ending for a film the size of this one could be a great opportunity for them to set up future sequels and spin-offs. The potential obviously is for something as cool as the ending for Empire Strikes Back. Something great enough to make the general audience satisfied, but puzzling enough about the future of the characters and potential future ordeals to leave both fans and the general audience wanting for more.