Would need to know more about a potential metroid game before I make a guess (oops, 'prediction')...ie who's gonna develop it.
I'm sure if it was developed by retro, it will be more like to sell than if it's developed by team ninja (just as a hypothetical example)...so it's a difficult one to just call without more info. I do believe pikmin 3 will sell more than previous pikmins though, even if it's not huge. Don't know why.
(slightly off topic I'm still living in hope for a new 2d style metroid game on a handheld at some point)







