The template for SSB 3DS is already done with Brawl and Melee, so all Nintendo would have to do is retool those engines with new features and characters and have a simple gameplay footage in several monsths. However, the Wii U version will have to be built from scratch and the CG video I was refering to would be similar to the Zelda Wii U trailer back at E3 this year.
Once
again, Sakurai has said that
no work on
either version will start until Kid Icarus is done, and the plan is for
both versions to go into production simultaneously. I wouldn't be surprised if Nintendo wanted to try connectivity between the two versions, or even online play between owners of different versions.
The "template" for Smash Bros. is nowhere near done. Sure, they know generally what kind of game they're going to make based on previous incarnations, but that's only a first step to creating a Game Design Document. And somehow I get the impression you have no idea how much time; effort; and manpower goes into creating one of those, and that work on the game
does not start until this document exists. These documents can take months to make, and then there's modeling the characters; the stages; the items; the specials; in-game physics; collision; never-ending bug testing; etc.
And all of that is assuming that everything is going according to plan, which is rare with game development. Point is, there's too much work for anything beyond pre-production to be show-able at E3 next year. Expect a CG or teaser trailer using pre-production artwork and legacy footage from Brawl and Melee.
And, incidentally, you don't want to see what a game looks like in its first few months of in-game assets. You
really don't.