A Geeky Viewpoint

Talking to comingsoon.net Simon Kinberg revealed the next X-Men film will be set in the 1990's.  

In 1991 Marvel revisioned the X-men in to separate comic books, The Uncanny X-Men chronicled the storys of the X-Men lead by Storm while the X-Men [comic book] followed the blue team lead by Cyclops.   The new comics brought in new costumes and new story lines and were some of the most successful comic books in history financially.   The X-Men issue #1 sold an estimated 3 .5 million copies and marvel shipped nearly 8 million copies making I the largest selling single comic book of all time.

There is no indication on whether Simon Kinberg was referring to X-Men: New Mutants or the untitled X-Men 7 film rumored to be in pre-development.

It should be noted that 20th Century Fox has already booked time at the same Montreal Studio that Bryan Singer filmed X-Men: Days of Future Past and X-Men: Apocalypse.   Bryan Singer has recently noted he wanted a crack at the Dark Phoenix Saga.

It is believed that most of the reoccurring cast from second trilogy, James McAvoy, Michael Fassbender, Jennifer Lawrence, and Nicholas Hoult, all signed 3 movie contracts which would be complete with X-Men: Apocalypse.  The cast from the original trilogy, Patrick Stewart, Ian McKellan, Hugh Jackman, Famke Janssen, Anna Paquin, Halle Berry, James Marsden and Rebecca Romijn signed individual contracts for each movie they have appeared in.

Hugh Jackman has indicated that he is retiring after one final outing as Wolverine in the untitled Wolverine Sequel currently filming.  

Ryan Reynolds character Deadpool, would be difficult to incorporate into a X-Men film according to Bryan Singer.   One would have to imagine it would be even more difficult set in the 1990's.