Umm Build your own charachter mode would be nice, don't you think?.....
Also like I said before, every character should be able to transform into different modes. For example, young link, by pressing the c-stick left/right/down(or on whatever other analog stick they include in the GC2 controller) young link transforms into a goron, deku, or zora ala majora's mask. Each come with there own specific traits and moves, for example deku would be fast but weak but he could float for long distances and shoot stuff, goron slow but powerful, zora average. Another example could be Mario (with all his hats or somthing). Now if you do that with every character, you would have a very nice strategy implemented. Not everyone will transform though, such a Samus. She won't transform but she can change her gun or something.
I think if HAL spent time on this and took a great deal of care, they could make SSM more than a legend in the gaming world. Also, LAN would be great but hard to implement. The levels would have to be aleast 2 times as big as Hyrule Temple and the camera would have to focus on your player alone some how for it to work.