The Wii U will close the gap and potentially pass the Vita, but the lead may not be sustainable with the announcement of the next generation Nintendo console imminent and the presumably long Vita shelf-life.
Nintendo has been relatively conservative with the Wii U release calendar. Even with sluggish console sales, games like New Super Mario Bros. U, Mario Kart 8, The Legend of Zelda: Windwaker HD, and Super Smash Bros. are financially safe releases. We even had a few niche titles like Pikmin 3 and Kirby and the Rainbow Curse. But everything changed with Splatoon. Splatoon revitalized the Wii U game library and appealed to an entirely new demographic; the last shooter I remember Nintendo pushing was Goldeneye 007 for the N64. Super Mario Maker is poised to be Nintendo's answer to Minecraft and I expect it to have an even greater influence than Splatoon. These are the types of games that will retain the fanbase and interest new players.
The Wii U is also in the midst of a remarkably strong release calendar. Although StarFox Zero and Yoshi's Woolly World probably won't have the appeal of Splatoon and Super Mario Maker or the sales consistency of Mario Kart 8 and Super Smash Bros., I expect them to sell at least 1 million copies each. Xenoblade Chronicles X will sell modestly. Together these games will generate Wii U sales.
Watch out Vita, it's going to be a big holiday for the Wii U.










