Madelyn Wils, president and chief executive of the Hudson River Park Trust, wanted to improve on a 2005 design for the pier. Needing private financing, she invited Barry Diller, the chairman of IAC/InterActiveCorp, with headquarters nearby. “I was interested if it could be more ambitious both architecturally and as a performance space,” Mr. Diller explained. They were smitten with the Heatherwick Shanghai pavilion. (Mr. Diller called it “the most incredible thing I had ever seen.”) Though they considered Santiago Calatrava and Bjarke Ingels, of the Copenhagen and New York firm BIG, Ms. Wils and Mr. Diller hired Mr. Heatherwick after hearing him discuss ideas. “It was clear the project was going to be his,” Mr. Diller said. “That’s what begat something more than a pier with shrubs.”