Though still not officially acknowledged or announced by 20th Century Fox, "X-Men Supernova" might tackle the "Dark Phoenix" arc of the X-Men franchise, and will start filming in the summer, in Montreal.
"X-Men: Apocalypse" was sort of a letdown from the successful X-Men movies. Fans are attributing the lukewarm reception it got due to the incomprehensible continuity of the MCU, which should merit a reset for the franchise.
According to Screen Rant, production rumors started floating that a new X-Men movie was in the works. Initially tagged with a working title of "Dark Phoenix," latest reports indicate that the movie's working title has been amended to "Teen Spirit," after the 1991 Nirvana hit song "Smells Like Teen Spirit."
Reports also indicated that "X-Men: Supernova" is set in the 90s, immediately following the 80s set "X-Men: Apocalypse." As said, the original working title would revolve around the "Dark Phoenix" arc basing on the working title and the story synopsis that was released. However, the change in working title seems to indicate that a change in the story might be in the offing as well, or it could be just to connect to another mutant movie or to avoid too much furor during the shoot.
Reportedly, "The New Mutants" will also start filming in the summer in Montreal. According to Comicbook, this would mean that the two X-Men movies would be filmed alongside one another. Another speculation floating is that there could be a crossover between the two film projects.
In comics, "The New Mutants" is based on the X-Men comic spinoff following the reintroduction of teen X-Men characters. It is not far-fetched to speculate that "The New Mutants" and the "X-Men: Supernova" are filming alongside each other for a remote possibility that they might share cast members.
The disappointing portrayal of "Dark Phoenix" in "X-Men Last Stand" was somehow softened by a younger Jean Grey, played by "Game of Thrones" star, Sophie Turner, who was shown already possessing the Phoenix force in her. If comic book canon were to be followed, this would mean the team has already been to space and met personas of the Shi'ar Empire.
In addition, the "Dark Phoenix Saga" has had Jean Grey, possessed by the Phoenix force, consumed a star to rejuvenate her powers, a star that has living planets in its solar system. What better way to confirm speculations that indicate writer/producer Simon Kinberg was pondering to reboot the entire X-Men franchise?