Right now, Wii U is behind the GameCube. I think it will pass it up eventually. Let's look at Nintendo's numbers for each console.

The left year will be GameCube/right  will be Wii U

FY 2002/2013   GCN- 3.80m /  Wii U- 3.45m                           

FY 2003/2014    GCN- 9.55m  / Wii U- 6.17m                Growth    GCN- 5.76m /  Wii U- 2.72m

June 30 ending 2003/2014    GCN- 9.63m  /  Wii U- 6.68m                 Growth   GCN-  80,000  /   Wii U- 510,000

Now lets look at future GameCube numbers... left will be LT numbers and right will be growth.

September 30th 2003- 10.45m/ 0.81m (price cut to $99.99)

December 31st 2003- 13.94m/ 3.5m

Now end of year numbers

December 31st 2004- 18.03m/ 4.09m

December 31st 2005- 20.61m/ 2.58m

December 31st 2006- 21.52m/ 0.91m

December 31st 2007- 21.74m/ 0.22m

Here's what I think Wii U numbers will be

September 30th 2014- 7.29m/ 0.61m

December 31st 2014- 10.73m/ 3.44m

Now end of year numbers.. I think Wii U will have a 2015 peak, 2016 similar to 2014, and 2017 to begin the true fall of Wii U sales

December 31st 2015- 16.80m/ 6.07m

December 31st 2016- 21.69m/ 4.89m

December 31st 2017- 24.09m/ 2.40m

December 31st 2018- 25.45m/ 1.36m (release of new console)

December 31st 2019- 26.02m/ 0.57m (probably last year of Wii U)

My prediction may change in the future but based on current sales.. this is what seems likely. I will make another one of these in late 2014/early 2015 if I remember.. So I expect Wii U to pass GameCube sometime in 2016

POST YOUR THOUGHTS AND YOUR OWN PREDICTIONS IN THE COMMENTS BELOW AND VOTE THE POLL

EDIT: Even if 2015 isn't Wii U's peak year it will still pass up GameCube. 2014 has MK and SSB and other 3rd party games...

2015 has fucking ZELDA, Splatoon, Star Fox, more Nintendo games, Xenoblade Chronicles X, and more

So even if 2015 isn't the peak year it will be about the same as 2014. The only reason 2014 sales are really low is because the first half of the year was abysmal (almost as bad as 2013) now it has a new baseline thats twice the size of the old one. Next years baseline will be at least 50k and most likely 60k-70k. Now Wii U is even beating Xbox One weekly after Xbox One's pricecut. If you say because Mario Kart 8... MK8 gave it a permanent boost.. not a temporary boost like people were saying. Staying around 60k for over a month now. Didn't go back to sub 30k like people said.

Just making a point that even if 2015 isn't the peak year it will still most likely outsell GameCube.

Never

Weird that i agree with you, but this is what i think as well.

Dat optimism.

I knew you'd say that.

I voted for definitely not in 2015. Anything can happen, so I won't say it won't surpass the GC.

This is the Wii Us peak year. It can be found 200 dollas at some retailers and some even discontinued ordering the system. Nintendos two biggest games are coming for it this year as well.

At the current rate, and with the sparse game line up I think never.

What's going to drive sales to nearly double in 2015?

Lol, dunno why i laughed at this. 

OT: In the most likely club, it wont hit 20mil lifetime. There's a chance, just not a very good one. Nintendo would need to pull a miracle at this point :-/

End of 2015