"X-Men: Apocalypse" will be released less than two years from now but the timeline it covers is 10 years from the events in "X-Men: Days of Future Past." While it will feature the First Class cast, the film will include younger versions of Scott Summer aka Cyclops, Jean Grey and Nightcrawler.

There would presumably be more returning mutants, but these characters, aside from being fan favorites, will be integral to the story to some extent. Of course, the issue on recasting is another matter.

The setting of the story will be 1983 as revealed by writer Simon Kinberg in an episode of "The Q&A with Jeff Goldsmith" podcast. Thus, there would already be some changes right from the get-go. One of the important events in that period would be the institution of Xavier's School for Gifted Youngsters. Cinema Blend writes:

"Being set in the early 1980s opens up a lot of options for X-Men: Apocalypse, but easily the most significant is what can be done with younger versions of classic characters. Jean Grey, Cyclops, Storm and other notable mutants were all flocking to Xavier's School for Gifted Youngsters around that time period, and presumably part of the plot of the new movie will have them enrolling and learning how to hone their powers. There are some other elements to think about, however... "

Some of those elements deal with the "plotholes" of "Days of Future Past." One of the biggest points was the Sentinels. It was pointed out in different forums that stopping the Sentinels program would be very uncharacteristic of the American Government. Granted, they would not be used to hunt down mutants but it would be naïve to think Uncle Sam would scrap a useful program based on that invention for other purposes.

Bryan Singer has teased the opening scene of the movie via Instagram, as he is wont to do. The sneak peek shows that the first scene will feature "The Four Horsemen." As to who will comprise the roles of War, Famine, Pestilence and Death, we can only speculate as of now.