Pending director Bryan Singer's departure from the eponymous franchise following the theatrical release of X-Men: Apocalypse this May, there will undoubtedly be many questioning the direction that the X-Men film series will turn to in the seminal filmmaker's absence. While there have been well-liked X-Men movies that have not been directed by Singer, it was largely by his hand that the Marvel Comics cast of characters became big screen fan favorites for general audiences at the turn of the century (thus ushering in an age of superhero movies to match and outpace them).
Following the release of the second Apocalypse trailer, and the film's cast having taken over the latest cover of Empire magazine, it seems that Apocalypse could end up concluding Singer's time on the franchise with a bang - unless he makes more X-Men films thereafter, as rumored. Either way, Singer already has an idea in mind for which X-Men comic book villain he wants to see utilized on the big screen next.
Speaking to Empire Magazine (via Heroic Hollywood), Singer was quick to discuss the implications of the ending to X-Men: Days of Future Past, namely in the reappearance and reintroduction of the Weapon X program, and all of its associated heroes and villains. It's already well known that William Stryker will return in a larger role in X-Men: Apocalypse, but what could come after Apocalypse is perhaps of greater note - as Singer, when asked about which villain he'd like to see in the X-Men series next, told Empire the following:
"I’d love to use Proteus somehow. There’s a lot visually you could do with a character like that."
Fans of the comic books no doubt remember Proteus, born Kevin MacTaggert and often christened with the nickname Mutant X, as the reality warping, possessive antagonist created by Scottish genetic researcher Moira MacTaggert (a character that Rose Byrne is playing again in Apocalypse) and her politician husband Joseph MacTaggert, whose abilities were so devastating to those around him that he was largely confined to live in seclusion at his mother's Muir Island research facility. Given the relatively obscure nature of such a character to general audiences, and coupled with the decided aesthetic appeal of Mutant X's particular powers, there could certainly be something novel to be made of said super-villain's inclusion in subsequent X-Men films - though how popular a concept Proteus might prove to be in the long run with fans remains to be seen.
In the meantime, the ultimate fate of Hugh Jackman as Wolverine is still largely unknown, with Singer having told Empire that "[as a] central character, he didn’t fit into this particular story" in Apocalypse - meaning, Wolverine 3 may be both the next and final appearance of Jackman in the role. However future installments in the franchise turn out, X-Men: Apocalypse will be the final production that Singer will lend his creative voice to, which turns out to be something of a blessing in his eyes - since, as he put it:
"I could not roll into another X-Men movie tomorrow. And I hope not to. I hope to take a break."
X-Men: Apocalypse will see theatrical release in the U.S. on May 27th, 2016, followed by Wolverine 3 on March 3rd, 2017, and unannounced X-Men films on October 6th, 2017 (possibly Gambit), January 12th, 2018 (possibly Deadpool 2), and July 13th, 2018. The New Mutants is also in development.