It depends. If the first few months with 2013 are littered with announcements for new iphones/samsung phones/next box etc there is a chance that the wiiu could sell less then 7m. A slim chance though as it's already hit 2m. I estimate that the life sales of the WiiU will put it somewhere inbetween the GC and N64, as long as 2013/2014 sees another console release and a continued popularity in iPhone/Nexus/etc products.
I actually don't think those things will matter very much. The people that want a Wii U are not going to suddenly decide not to get one just because some new phone (with the tiniest increase in something new over the last phone ) was announced.
New console announcements....maybe. But largely it seems that consoles sales tend to be not be deterred too much by competitor consoles these days. All 3 last gen consoles over 70 million.
The thing is you have to consider who wants a wii u. All I can think of is die hard Nintendo fans. Anyone who is a casual who enjoyed the wii is probably more inclined to play on a tablet/phone then cash out on a console. Are there really many die hard Nintendo fans left? The Wii would have deterred many new potential fans by offering the least of the 3 systems, meaning that gamers will most likely already have a 360/ps3, and therefore why upgrade to something which ash the "tiniest increase in something over the last" console?
While it may be amazing for you to believe, most gamers aren't interested in this "tiny increase" you are talking about, which i'm assuming you mean processing power. A lot of gamers will buy the Wii u for its Nintendo franchises, others will buy it for its innovations, something you won't find elsewhere.
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In my opinion the N64 was not just the best console of the 5th gen but, to this day the best console ever created!