Well storm is part of the X-men franchise which fox still owns the rights to and they have been more interested in milking Wolverine for everything his worth rather than exploring the other characters in the X-men universe.

Maybe now that Logan has closed that chapter they'll move onto others like Gambit, Jean & Cyclopse.

They already recast storm in the apocolypse movie so im sure you'll see more of her in phoenix but as for a solo movie you'll have to wait

Marvel are looking at doing their first female stand alone movie in Ms Marvel and also Wasp will be featured in the new Ant-man