I can't imagine what Nintendo could possibly do for the Wii U that would allow that console to top the PS4. Their two best shots were Mario Kart and Smash Bros., neither of which have made the Wii U a hit. On the other hand, the PS4 is just getting started.
Xbox One winning the US is more likely. Microsoft could still break open the vault and buy something massive. It's unlikely, sure, but it's more realistic than Nintendo doing the same in Japan.