Well, it was apparently revealed that it was in the works at E3.
I'm very excited about this. It's returning more to what metroid should be it seems. Sidescrolling adventure, not first person shooter. But it also looks to have some FPS elements in it too.
If it's as good as this preview makes it look, then Wii owners should really have something to look foreword to.
(Team Ninja was behind the Ninja Gaiden games.)
If you don't trust a youtube video, Here's a more official link.