Although I still expect to see them as an AT, I had a great idea for the dynamics of a playable Ouendan/EBA.
Instead of having three characters who all perform the same move (like the Ice Climbers), imagine that you have three characters standing shoulder to shoulder and when a move is performed, they all perform a different action which still falls within the context of the move.
For example, When you Up smash, the left guy swings his fist up at an angle from the left, the middle guy thrusts his fists straight up, and the right guy swings his fist up from the right. The characters would work together to cover as much area as possible with each move, such as a down smash causing the left and right guys to leg sweep their respective sides while the center guy attacks the ground immediately below him.
Thus, as the characters are KOed individually, the area covered by the moveset would diminish (with the center character being the key character). I imagine they'd still jump and move in perfect sync, but they'd perform different functions in each move.