Nintendo has been mum on the development of Metroid Prime 4 since its announcement at E3 2017, but it looks like development has not been going well. In a video announcement, Shinya Takahashi stated that Nintendo has decided to restart development of Metroid Prime 4 and hand over the reins to Retro Studios, the development house behind the first three Metroid Prime games.
https://www.notebookcheck.net/Development-on-Metroid-Prime-4-to-be-restarted-with-veteran-developer-Retro-Studios-at-the-helm.401371.0.html