no confirmation on platform though  (Gamecube or Revolution)

http://www.ga-forum.com/showthread.php?t=47385

quote:
 "Responding to a thread about Retro showing something at E3."


Quote:
      "Huh? Sounds suspect. Retro is working on Metroid Prime 3 for 
Revolution. Unless it has another game in the works, I just don't see how 
this information could be true."

      Matt



quote:

"In a thread about what he said in the other thread."

Quote:
      "I should clarify that while Metroid Prime 3 is allegedly in the 
works, I'm not certain on the platform. I'm assuming that it's going to be a 
Revolution launch title. But I suppose it could be a very, very late 
GameCube project, too. Don't know.

      Sure be nice to find out at E3."

      Matt