Source please?
I doubt KH3 being exclusive to WiiU, but if it is true that there is something big happening, which is definitely possible, I think there are more likely possibilities.
Nintendo buys Sega: Let's just look at things for a second. Sega is doing horribly, they're a Japanese company just like Nintendo, since they went to software only a lot of their stuff has been on Nintendo systems, Sonic fits in perfectly with Nintendo's lineup (he was in Brawl after all), and it would give Nintendo access to more IPs. Considering the state of Sega, I could see it happening.
Nintendo buys Megaman: I suggested this over a year ago when it was announced that Legends 3 was cancelled. This makes a lot of sense to me. It's a beloved series which would cause a big blast if it became exclusive, Capcom obviously isn't using the IP anymore and doesn't think it will make them any money, Megaman began on Nintendo and fits in just perfectly with their entire line up, Capcom loves money, and Nintendo has the resources to and dedication to give Megaman a good home and support.
Nintendo buys (insert 3rd party dev/IP)
That's all I can really think of.