If a Wii U exclusive, it'll probably be an existing Nintendo IP. Platinum's greatest weakness is that they don't typically make games that sell a lot. The original Bayonetta was their best-seller of all time and still only sold about 2 million across two platforms. After Bayonetta 2 and Wonderful 101, I can easily imagine Nintendo trusting them with a valued name and Platinum looking for a partnership with Nintendo.
As for what Platinum could be working on, Star Fox is a relatively obvious choice, considering how little of that game has been shown and the interest Kamiya has shown in making a Star Fox game. That would resemble how just last year, Nintendo worked with Namco for SSB4.
Besides Star Fox, I think Platinum could be working on a Kid Icarus game. Seriously. With Uprising, Nintendo showed that they were willing to turn Kid Icarus into an action/shooter game rather than an action-platformer. Uprising's ground combat and most of its bosses were based around a combination of fast-paced ranged and melee attacks with a wide variety of weapons. I could easily imagine Platinum making a game like this for the Wii U, possibly including ideas from Vanquish.







