Giving the WiiU version legs over the 3DS will depend on a number of unanswered questions, such as "What modes and features will be WiiU exclusive," and "How will connecting the 3DS and WiiU versions benefit the player or enhance the experience." I'm sure the WiiU will have exclusive features, much like how the 3DS version has Smash Run. It's just a matter of what they are, and they probably won't delve into that until E3 at the earliest.