Snake would bring more hype for the Wii U version, especially if he's heavily marketed upon his reveal. And if they include the code for the 5 bonus characters free for the 3DS version, it'd be more incentive for 3DS players to get the Wii U version, & they could bypass the Cross-Buy stuff. Either way, my gut is telling me that if this leak is legit, the 5 DLC characters will be in the Wii U version to start with.
Why would a 3DS owner buy the Wii U game for the DLC? It would be significantly cheaper to buy the DLC separately..