A couple of million. Metroid more or less salvaged the cube (together with wind waker). Nintendo needs something similar now that it's clear the low tech pad isn't going to sway any casuals. I'm sorry to say the only people who care about DKC (like new Mario bros) are the ones that already own a Wii U, and want to have an extra game, maybe for their kids.Just how many more consoles do you think a Metroid game would shift - given the series' performance on both the Gamecube and Wii - compared to a Donkey Kong game?
Btw what I really think Nintendo needs is a new IP in the vein of Metroid, more so than a new (or 'New') Metroid. Something that feels grand, has mystery and is with aliens. The Wii U is irrelevant. People need something that makes it relevant. A new Mario or DKC is not going to provide that. They have those on the Wii and it's collecting dust.