The rumor is confusing anyway, Monster Games is the developer and Retro? Sounds like they're just assisting.
I don't even think it will end up being for the Wii U, probably smarter to move it into the launch window of the next-gen Nintendo handheld/fusion device (Mario Kart 9 is probably a long ways out).
If they could launch the next system with Mario Galaxy 3, Animal Crossing Next, and Diddy Kong Racing 2 ... it would make up for the poor 3DS and Wii U launches in spades.
I agree that Retro shouldn't do Metroid either though. I think they did their time on that IP and it's not something that moves Nintendo consoles either. Maybe let them make something new on their own.