2. How will the Wii U and 3DS versions interact?
Since Super Smash Bros. was announced, Sakurai has emphasized how important the connectivity between the Wii U and 3DS versions will be. In fact, he stated that the way the Wii U and 3DS versions interact will keep Super Smash Bros. from becoming a stale sequel with better visuals and a half dozen more characters.
For such an important feature we know so little about it. Sakurai has hinted character customization will carry across both systems, possibly affecting the gameplay of individual characters, and maybe dealing with cosmetic changes. And that's about it. Because both Nintendo had Sakurai have been vague about this feature, this unanswered question looms large.