It doesn't have to have everything smash bros has. I've thought about it, and if someone worked hard enough, they could make an epic smashbros style game. If Project GB was like this, I'd expect to see:
Multiple attacks
Tons of special abilities and items
Beautiful sprites
Customization for game goals, and rules, such as health, time, etc,
Tons of special effects and crazy mechanics and animations
etc.
Platform Builder is capable of all of this. I know it. It just takes a brilliant mind, and effort!