I think it would depends of what NX means.  Some are predicting it's a new console but it could also be a handheld.

But But But Gamecube!!

It's technically not impossible for things to turn around... But yeah, it's a pretty safe bet.

isnt nintendo mini worse

My theory is its both. Same games, running on both a consol and a handheld, with varying resolutions (much lower for the handhelds).

Which then results in Wii U sales crashing.

Well, i think that we already know this... any way, i predict that by 2016 the gap will decrease.
GC sales after 2004:
2005: 2,750,000
2006: 1,100,000
2007: 200,000

Wii U in 2016 - 2018 will sell better than this imo.

Nintendo has taken the profit over market share approach. Look at GameCube, 2 price cuts in 2 years and a $99 price tag, it still couldn't sell over 22 million.

Instead of fighting a battle that can't be won, Nintendo has decided to try making as much money as possible while pleasing fans by pumping out a handful of 1st/2nd party exclusives each year.

I think a price cut will happen in September, a $249.99 Mario Maker bundle. Perhaps another cut to $199.99 in May 2017 followed by its successor releasing in November 2017.

We still have Zelda, the inevitable Animal Crossing U (which will move a lot of consoles, especially in Japan) Maybe Metroid Wii U and who knows what else. Wait until after E3 to really decide if it will hit 20m or not. My prediction is it will sell more than GC but not by much.

If it's something like that, the sales will definitely drop like a rock.  I don't see Nintendo dropping Wii U prices significantly, at least not below $200.

The system has sold terribly but Nintendo can fall back on Amiibos and games to break even. Its a shame really, can you imagine all the money Nintendo would have made off Amiibo if the system was selling better. I just hope that they roll out NX and their next console with a better strategy and appropriate pricing.