Judging by the seats, perhaps making it as light as possible. Existing airframes are relatively light but let's be honest, they aren't trying to save 500g here and there when they have massive jet engines to get everything airborne.
Every kg saved is a kg more of freight that can be transported (or a little less fuel used to keep the plane in the air); save 500g for each seat of a 200-seat plane, and you can put one more paying passenger in the cabin.