Bryan Singer's X-Men: Apocalypse didn't exactly bring the X-Men: First Class movie trilogy (with Days of Future Past serving as the middle chapter) to a triumphant conclusion, judging by the overall mixed reception to the film. It certainly wasn't a low-point for the X-Men franchise either (as far as the critical reaction goes), and brought in over half a billion at the worldwide box office. Moreover, as far as the future is concerned, Apocalypse succeeded in introducing younger versions of numerous famous X-Men - Jean Grey (Sophie Turner) and Scott Summers/Cyclops (Tye Sheridan) among them - who could appear in one or more of the X-Men installments currently in active development.
The generation of X-Men who are only teenagers when Apocalypse takes place during the 1980s could have turned out a bit different, had casting not worked out the way it did. So much is illustrated by the newly-unveiled concept art for Jean Grey in the film, featuring Elle Fanning (Maleficent, The Neon Demon) in the role instead of Game of Thrones' Sophie Turner. Disney Channel star Zendaya was similarly in the running to play the young Ororo Munroe/Storm in Apocalypse, before Alexander Shipp landed the role and Zendaya instead went on to snag a leading role in another comic book film adaptation altogether (next year's Spider-Man: Homecoming).
Although there isn't official concept art available that shows what Zendaya as Storm could have looked like, the following piece of concept art created by Apocalypse's costume concept artist, Philip Boutte Jr. (hat tip to CBM), does reveal an alternate (in this case meaning "unused") look for the character in the film:
Storm's final appearance in Apocalypse isn't as significantly different from her look in Boutte Jr.'s concept art as Jean Grey's costume design in the film is from her own early conceptual design. Nevertheless, the character was originally designed to adhere even closer to the punk-rock sense of fashion embraced by her counterpart from the Uncanny X-Men comic books, compared to her final appearance during the movie. It's possible that Singer and his collaborators ultimately decided that this look for Storm didn't fit as well with Apocalypse's vision of the 1980s as the look that they went with, instead.
It's possible that Shipp's Storm will wear an outfit closer to her look in this Apocalypse concept art, in a future X-Men movie. Days of Future Past and Apocalypse screenwriter Simon Kinberg has confirmed that the next main X-Men film installment will take place in the 1990s, so young Storm may adapt her Uncanny look for that movie. The character is also heavily rumored to appear in the developing New Mutants movie, so that's another potential opportunity for Storm to mix up her attire accordingly.
Wolverine 3 opens in U.S. theaters on March 3rd, 2017, followed by unannounced X-Men films on October 6th, 2017, March 2nd, 2018, and June 29th, 2018. Deadpool 2, Gambit, New Mutants and X-Force are currently in development.