This is a just for fun one. I don't think a lot of these will make it and I think we will get significantly less new characters. There were some personal things I wanted to throw in but the current program doesn't offer. The bottom row is unlockables and the side bar would be returning veterans that would also be unlockable after the rest are unlocked.
The Female Trainer, I wanted to have starters from different gens not just Hoeen. Such as Piplup, Bayleef and Blaziken.
Midna/Wolf Link was supposed to be a transformation for Link.
Dixie- Instead of having just her they could have it work like Pokemon Trainer where you could switch(using a tag barrel) between Kiddy, Dixie and Funky.
Meowth- I always thought deserved to be in over most other choices and could be the "Villain" slot for Pokemon.
Zelda/Impa- Get rid of Sheik and just have a fixed Zelda that isn't completely useless. Impa essentially becomes a more powerful/useful Sheik.
I hope sakurai allows for more fan interaction with Brawl and character requests. If I remember correctly he only took Japanese fan character requests last time. I also hope he continues to offer surprise characters as well such as Snake & Pokemon Trainer in Brawl.