IMO it's got a great line-up of exclusives dropping in 2015, there are plenty of reasons for people to buy the system.
Nintendo has never released a new home console a mere 4 years after the last platform they launched, and 6 years after Wii U came out there will be some very impressive tech on the market for them to choose from at a very reasonable price to them (new AMD CPU cores for an APU, new GPU tech, HBM and a choice of either stacked DDR4 or fast Universal Memory), plus that will be a year before the next Playstation and Xbox systems drop, so they're in a position to lead with revolutionary tech that both Sony and Microsoft will have to use.
Nintendo will hold out until 2018 to launch their next home console, so we're looking at another 4 years of software support for the Wii U.
I doubt the platform's peaked, I think Nintendo has at least one more 3D Mario game, another Zelda after the one landing in 2015, other new IPs (not only from existing franchises) like Splatoon, some sequels and probably some exclusives indies too.
I think Nintendo has other partnerships like Devil's Third in the pipeline too.
We'll probably see a comeback of Metroid, sequels for DK, Pikmin, maybe a Pokemon (in which case sales will sky rocket). People like to forget that Nintendo has other games like Wave Race, F-Zero, Pilot Wings that target different audiences to the ones they've already released games for and they can be very creative with new games.
IMO over 30 million is very likely for Lifetime (only one Nintendo system has sold less than that), I think Wii U will top 14 million by the end of 2015 and peak in 2016 selling over 21 by the end of that year, with a couple of 5 years after that.
There's plenty Nintendo can do to drive the sales of Wii U up much harder than we've seen, not forgetting great bundles with big games like MK8, Smash.
