*spoilers* ahead if you don’t want to see anything, I’d advise refraining from clicking on the links below.
GameXplain uploaded the end to Metroid Prime:Federation Force, in a post credits scene, you can clearly see that they are teasing a brand new Metroid game. The video in question includes the entire final mission, boss, and ending of FF, but I included a time stamp to avoid it. Refrain from watching in any case if you want to see it for yourself.
GameXplain uploaded a video discussing it.
If you don’t want to see the video, here are screencaps