When Legendary Pictures first acquired the rights to make a film based on the Pokémon license, most fans expected something based on the main series of games. Instead, the studio surprised everyone by basing the film on Detective Pikachu, a spin-off game that, at that point, had not been released outside of Japan. While the film is still a few months away from release, it seems clear that Legendary seems confident regarding Pokémon: Detective Pikachu‘s success. So confident, that the studio is apparently already planning two spin-off films.
One spin-off will apparently be based on the first generation of Pokémon games (Red and Green in Japan, Red and Blue in other territories). Additionally, a film centered around Mewtwo is also in development. It should be noted that these are rumors, at this time.
We’ll likely have a much better idea on future plans for the film franchise depending on the performance of Pokémon: Detective Pikachu both critically and commercially. Stay tuned to Nintendojo for more as it develops!
Source: Comic Book Resources