In a new interview with Fandango, Singer revealed the following:
I imagine—and this is the first time I’ve actually answered the question this way—but another thing that’s been introduced in the comics is a big alien, interstellar tenant within the X-Men universe that hasn’t been explored. And to me, that might be kind of fun because I’m a huge Star Wars and Star Trek fan, and exploring the X-Men universe and being able to utilize that would be exciting, visually.
Besides disappointing fans hoping for a showdown with Sauron, the evil half-pterodactyl, Fandango speculates this mysterious space-based storyline will be the famous “Dark Phoenix” arc, in which (very mild spoilers for a comic book narrative that may or may not play a role in the next movie) Jean Grey goes to space and runs afoul of the Shi’ar Empire, an alien society that often appears in the X-books. While this might be fun for fans who resent the way X-Men: The Last Stand barfed all over the Dark Phoenix mythos, for Singer it seems to be more about aesthetics. “Like Apocalypse—like some of the imagery and characters and stakes [in that movie]—it’s something we haven’t seen before,” he adds. “If I’m going to be involved in a significant way, it has to be something different. Visually different and aesthetically different.”
There are certainly a plethora of stories to borrow from if the X-Men are going to space in the ’90s, however. It doesn’t have to be the Dark Phoenix saga: It could be the “Unstoppable” arc from Joss Whedon’s Astonishing X-Men run, where they travel to the Breakworld. Or maybe it’s that time they journeyed to the stars to fight the techno-organic aliens known as The Phalanx. One thing is certain: Earthbound baddies like Forearm, a.k.a. the menacing villain with, um, a really big extra pair of arms, will have to spend the film on the sidelines, moping around the third planet from the sun.