When the Smithsonian introduced a futuristic plan for the 17 acres around its iconic administration building, the National Historic Landmark known as the Castle, officials predicted it would be a game-changer that would remake the structure into a visitor gateway to the storied institution. Six years later, a new Smithsonian administration has jettisoned the eye-popping elements of the $2 billion design by Danish architect Bjarke Ingels, opting instead for a dramatically downsized version.