Both writers are currently in negotiations to write the script for the Pokémon flick, which is said to be based on the Detective Pikachu game for 3DS. Curiously, it has yet to receive an English release.
With a quirky and accessible series like Gravity Falls under Hirsch's belt and the massive success of Guardians of the Galaxy for Perlman, it seems as though this Pikachu-focused movie is actually in great hands, though it's hard to say what about Detective Pikachu could actually constitute a movie. Why not a full-length Pokemon-only movie to keep options open?
Universal Pictures is going to tackle the film's distribution outside of Japan, and The Pokemon Company's collaborator Toho will handle distribution inside of Japan. There's no set release date for the film just yet, but you can bet there'll be plenty of news leaking out with the popularity of Pokémon Go and Pokémon Sun and Moon releasing later this year.