Not that I haven't seen wonderful opera productions done with just piano - in my youth, the Hartt school did excellent "touring opera" productions, and there were reputable small companies in the Boston area such as Longwood Opera. But NYCO, in a now very rare appearance? That's too bad. Perhaps it's time to rename themselves and start over?
Among the operas I saw the Hartt school do with solo piano was The Love For Thee Oranges. As a young pianist then, I was absolutely amazed that anyone could play that score on piano seemingly so effortlessly. I think I still would be amazed. :-)