Soundwave on 07 August 2014
I'm gonna say never, barring a miracle (like Splatoon becoming the next Pokemon or Wii Sports).
The GameCube is actually going to increase its lead over the Wii U this year, because holiday 2003 was the GameCube's biggest holiday season. It had a huge spike thanks to a price cut to $99.99 and the November launch of Mario Kart: Double Dash.
2003 was the only holiday season where the GCN beat the XBox.
So Wii U will continue to lose ground for the rest of the year.
I don't think Zelda U will cause that big of a bump either. It's not a big IP in Japan anymore, and isn't huge in Europe either. And Hyrule Warriors + Smash + Wind Waker HD will probably already bring a lot of the Zelda fans over before hand anyway.
