His latest project for the Hudson Yards on the Far West Side of Manhattan may become a new city landmark; for now it remains shrouded in secrecy. Stephen M. Ross, chairman of Related Companies, a Hudson Yards developer, compared it to the Eiffel Tower in Fortune magazine two years ago, but one person who saw the design at that time described a concept much more grandiose than the developers’ original idea for a sculpture on a plaza fronting Hudson Yards’ vertical mall. Mr. Heatherwick envisioned a “vessel” that could occupy a large part of the plaza, shot through with dozens of stairways. Shaped like a chalice, it would rise higher than the adjacent, cavernous Culture Shed, the 100-foot-high international arts center also planned for Hudson Yards. Related and the co-developer, Oxford Properties, refuse to discuss Mr. Heatherwick’s design.