It's an interesting question that I'm really interested in, interesting.

Since SSB is 4 player local the second screen on the Wii U can't be used apart from mirroring the TV. However SSB as of recently has started to make huge epic single player gameplay so maybe for the campaign the second screen will be used in an awesome way. If that is the case, I could see the 3DS version being the Wii U campaign with cross-save and then having its own multiplayer "element."

Or if both versions are fairly similar, I'd just prefer the 3DS to have a 1 to 1 port. Contrary to popular belief PSASBR is great having it on both a home console and a handheld so this would be better than the 3DS getting an inferior version.

This would be .. amazing and beautiful. 

I only hope that if they do keep the same visuals for both 3DS and Wii U.. that they won't make the Wii U's graphics "simpler" so that the 3DS could keep up. Sigh. 

I really believe will be different! But the thought of online(wii u) and on the go (3ds) is a dream come true!!! I want this so bad!!!

I hope the 3DS version is good, because I probably won't get a Wii U anytime soon.

WiiU gets Mario, 3DS gets Luigi!

I hope the 3ds version is playable on the normal 3DS. The screen is so tiny <.<

TheLastStarFighter said:
WiiU gets Mario, 3DS gets Luigi!

Keep the bros in the same game!!!
If they had exclusive characters though they should have handheld characters group from games on handhelds
EX: Pokemon(new pokemon i guess), Golden Sun (isaac), and Kirby (most games are handhelds)

I hope Nintendo doesn't decide just to remake a previous version in 3D like Star Fox and Zelda. It would be cool but I think people are looking to play something new.