It will do it by the end of 2015. 6m+ lifetime and 7m+ with some luck.

Not a flop
it is a shame since it is a great amazing game!

DLC shoudl help and Amiibo support maybe re bundle the game with Limited(to the bundle) Cat mario - Cat Peach - Cat Luigi and Cat Toad.

Yes it can and it will. The attach rate of the Wii U is something that shouldn't be under estimated.

For sure if Nintendo will release a "select" version of the game.

Most likely... if the Wii U has a boost in sales, then even more so

The Wii U attach rate isn't exactly remarkable.  5.75 so far.  At the same time in their lives the Wii was at 6.94 and the PS3 was at 7.39.  That's even considering the fact that a much larger percentage of the Wii U userbase were early adopters compared to the Wii and PS3.  33.3% of Wii U shipments were in the launch quarter.  In comparison the Wii was 7.1% and the PS3 was 8.1%.  All numbers based on shipments, so that also includes digital sales of disc based games for Wii U.

As for the topic, considering the bundle is still available (and in the US seems to be the only way to buy a Wii U), it should have no problem reaching 5 million.

Bundles and price drop will help it reach it.

You know what would be awesome? If it would outsell Sunshine!

I think 5m is pretty doable, especially with price drops to both the Wii U & 3D World. 3D World is one of the more visible exclusives for the Wii U, so I feel most people buying a Wii U will be getting the game at some point.

It'll easily do it, unless something catastrophic happens.