Considering how many things Nintendo did wrong with the  WiiU, reaching N64 numbers would quite the achievement if you ask me!

just have bayonetta in adult themed commercials 

1 million sales right there XD

In those commercials they should highlight Bayo's butt as many times as possible.. They will surely lurk in all  those thirsty gamers..

It ought to easily pass 20m imo. Seems a given. Anything beyond that is just too speculative and mainly depends on the effect of things like Smash Bros., Amiibo and the sales and impact of future releases, both announced and unannounced.

I never make predictions on total console sold through their life time, but I think that as ball parks:

1 - The PS4 will lend somewhere between PS1 and PS2 sales total, depending how long the gen last (PS2 reached 150 million pretty fast)

2 - Wii U and XB1 are much harder to predict, I see them hovering between game cube and N64 levels (20 - 45 million units each) I am still not sure which one will sell more or even if they will both sell essentially the same amount of units.

What could change this:

MS or Sony revealing that their console architecture was designed to be scalable from the get go and they release an upgraded version in 2 or 3 years (upgraded = faster CPU/GPU) that runs the exact same software, games and OS, just faster.

People really like Halo 5 and it changes everything (not gonna happen, Halo is not unique enough to do like Mario Kart or a new Zelda titles does for the Wii U).

I predicted 18-22 million. I still think it'll be between that.

My prediction is what he said -  if I ever predicted lower for the Wii u it would have been 17 - 22 million 

I would stand behind either prediction (20-25 million or 17-22 million).  

Number of Wii u s sold till the next console is released 

Everyone expected the Wii u to perform better once Mario Kart came out and it has-  probably not as well as many thought earlier but it is doing better-  but a boost via MK8 then Smash and future big release are and always have been expected so I don t see any reason to increase earlier predictions for the Wii u lifetime sales ( till it's successor is realeased)

I myself predicted 15 Million to my horror as a Nintendo fan. Sure it's looking up at the moment.
I would love to be wrong though :).

It will sell more than the gamecube. How much i don´t know.

i predicted 15M, im obviously a lot more hopeful a month after Mario Kart, but there far from out of the woods yet.

But dont ever get me wrong i never hoped for 15M, i hope they can be as successful as the original Wii. 15M is not an unrealistic estimate based of Nintendos very own forecasts.

Even 20-25m would be seen as a dismal failure, so yeah lets all hope for a lot more, but lets also be realistic and not count to many chickens just because of a month follow Mario Kart, where sales have gone from crashing and burning to mediocre.