Wii U will probably hit its forecast, possibly by the end of the calendar year (it's pretty conservative at 3.6m) Wii U is tracking 350k above this time last year, which managed to do 2.9 Million on an abysmal software lineup that makes this year's look like the height of the PS2 calendar.
So 10m is a complete joke, told by Dane Cook, as Wii U should pass 10m spring next year.
2015 will likely be its strongest selling year, not by too much, but I imagine 4 million for 2015 is a nice safe number (remember there is likely a price drop for the Wii U in 2015 as well) leaving the Wii U just shy of 14m by the end of 2015(fy) if the next 2 years lose 50% YOY, you'd see it at around 17m by 2017, This just takes into account Wii U not really having any surprises and amiibo being a complete bust as a system seller (which it might be). People who think it will outsell Gamecube, expect Wii U to have a surprise system seller or two, it might just do that but ending short of 15m is extremely unlikely, even more unlikely than it passing Gamecube numbers IMO.