If the Wii U was launching with a Perfect Dark game, I think it'd almost certainly be the no.2 best selling game after Mario.
But there are few other possibilities that would be fun to speculate about:
Killer Instinct Returns - Given the resurgance of 2D fighters (Street Fighter, Mortal Kombat somewhat), a new KI could really kick ass.
GoldenEye/007 - I think Nintendo + Activision could work out a deal where Rare could develop 007 games, including a "real" remake of the original N64 GoldenEye for the Wii U. Activision and Nintendo share the profit, Nintendo fans get exclusive content.
Donkey Kong Country U - Now that Retro is working on something seemingly original, DKC could shift back to Rare. Re-hire David Wise for the music too.