I'd say the Wii U has no chance of getting past the Gamecube. Thats still over 12 million sales away. Even if the Wii U from here on in was to average 50,000 a week worldwide (which in itself is VERY optimistic), that still means its got to do so, for 240 more weeks. Thats well over 4 and a half years! The Wii U will not be still on the shelves in 4.5 years time, that much is pretty much certain. The Wii U is destined to become the worst selling Nintendo console of all time.
PREDICTIONS FOR END OF 2015: (Made Jan 1st 2015)
PS4 - 34M - XB1 - 21m - WII U -12M