Director Bryan Singer revealed via twitter that following the release of 2014's Days of Future Past, the next X-Men film to be released will feature Apocalypse. More recently, the rumor has spread that it will also be set in the 1970's and further develop the younger iteration of the team.
Via Screenrant:
Out of the blue, X-Men: Days of Future Past director Bryan Singer revealed last week that another franchise installment is coming in 2016. The X-Men: Apocalypse teaser preceded news that co-writer Simon Kinberg had signed a three-year deal with Twentieth Century Fox to help guide their own Marvel Cinematic Universe by writing/producing stories that span multiple films.
It all begins with Days of Future Past next summer, a time travel story that involves both the casts of the original X-Men trilogy and the younger cast from X-Men: First Class. Rumors last week pointed towards X-Men: Apocalypse serving as a direct followup that would aim to bring back nearly everybody, along with a few new faces, but as we learned today that may not be the case.
Variety has the scoop on Bryan Singer returning to direct X-Men: Apocalypse which comes as no surprise since we heard previously that it was him and Kinberg who were already planning out what the next X-Men team-up would be about. What is surprising is that they claim to have confirmed that X-Men: Apocalypse will be strictly set in the '70s following the events of Days of Future Past, meaning no post-apocalyptic future and original X-Men returnees. This directly contradicts Bleeding Cool's insider who claimed future/present team members would be back as well. At this point, it's all unofficial and a lot of the rumors sound increasingly like speculation.
If Variety is correct however, this answers the question about how Fox will get the entire cast to return since if it's focusing mainly on the First Class stars, they all initially signed with multi-picture contracts for a trilogy. Think of Apocalypse as X-Men: First Class 3 and think of Days of Future Past as a big budget investment (possibly the most expensive superhero film ever made) as a way to boost the brand appeal and box office results, leading into Apocalypse.
Introduced in the pages of X-Factor back in 1986, Apocalypse has become a cult supervillain for fans of the mutant comic book series. While he was simply a super powered evil mutant at first, he later became much more important. He was also the central threat to an alternate reality explored in Age of Apocalypse, a Marvel Universe without Professor X.
Properly handled, he could be a feature film villain that would equal Thanos in Avengers.