I'm calling it now, Wii U's peak will be higher than GameCube's peak. GameCube peaked in the fiscal year 2003 with 5.76m units sold according to http://vgsales.wikia.com/wiki/Nintendo_GameCube, and I'm predicting next year that Wii U will sell anywhere from 6-8m units. Really hoping for 8m+, but 6m is forseeable. Anyway, I think in fiscal year 2015 that Wii U will sell over 6m units, beating the GameCube's peak, and then eventually beating the GameCube lifetime.
XBOX ONE/Wii U/3DS/PC
RIP Iwata 12/6/1959-7/11/2015
Thanks for all the great memories!