Assuming it's Wii U-bound, there really not much work they need to do for asset creation, or any substantial engine work. If for nothing else, it would be a much cheaper game than a ground-up Metroid from any of their studios.
Even a NX-bound version would probably not require much work; just up the resolution and the framerate and you'd be pretty good to go.
The longer they wait to do a Metroid, the more expensive it's going to be to make, and the harder it will be to sell.