Most superhero franchises, no matter how grand and large-scale they appear to be, always build up to one massive event. Case in point: the Marvel Cinematic Universe started out as origin stories of each Avenger member and is now leading towards the "Infinity War." "X-Men," on the other hand, has constantly surprised fans with its seemingly unpredictable path; however, it appears that "X-Men" is taking on one definitive track for its future films: "The Dark Phoenix Saga."
It's been talked about before "X-Men: Apocalypse" that the mutant franchise might lead towards a story arc that would focus on Jean Grey and her transition into Phoenix. In the movie itself, viewers got a taste of Jean's massive powers.
It should be remember that 20th Century Fox took this route during the 2006 movie "X-Men: The Last Stand," at that time Famke Janssen's Jean Grey lost control of her growing powers and she eventually became a villain. The movie wasn't received well.
With the reset happening in the newer "X-Men" movies that started with "X-Men: First Class," it's possible for the studio to redeem themselves at this joint. Moreover, "X-Men: Days of Future Past" basically wiped out the entire timeline of the original "X-Men" trilogy, which means the upcoming films can start fresh, with Sophie Turner at the center as Jean Grey.
According to Movie Web, Bryan Singer said "X-Men 7" will partially take place in outer space and that the movie will be set in the 1990s. In the comic books, the Phoenix Force is a separate entity that comes from outer space. When Jean was on a mission in outer space, the Phoenix Force found her and took note of her unparalleled potential.
The reboot is also a likely result the ageing mutant movie series. For one, Hugh Jackman is retiring as Wolverine, with "Logan" her last outing as the mutant. In the movie, Professor X also appears much older, and both characters see their powers dwindle. With this, a reboot can only be expected. According to The Hollywood Reporter, source says the "X-Men" franchise will be reconfigured, with Simon Kinberg overseeing the franchise as producer and writer.