Nintendo recently re-launched the official Japanese Metroid page with information on each of the Wii ports of GameCube titles Metroid Prime 1 and 2. More interesting, though, is a teaser at the bottom of the page that reads "Another Side Story." A caption is provided below, which loosely translates to "Experience the backstory of the Space Pirates."
What could this mean? Is extra content on the way for Metroid Prime 3, or is Nintendo planning a new Metroid game altogether? Possibly, but others have surmised that it may not be a game at all, but rather a continuation to Nintendo's e-manga comic book, which deals with Metroid lore.
All factors considered, it's probably the latter, but a Metroid game that places players in control of the enemy faction would be rad - no doubt about it.