First off, I like to say that Sesame Street in suppost to be represent a real inner city, New York City street,which many in New York are very diverse. Second, I'd like to say that America is even more diverse then it use to be, and I think the point that Hays was trying to make here is that, even thow you cannot possibly fit every single culture on the planet on the show, they could have some characters on the show(Like maybe a family or something) to acknowledge that this is whats happening in this country today, especally in New York.
Besides, not only is Sesame Street about change, But the show has new characters all the time. It has been noted by the people at Sesame Workshop that the show is a brand new show every year, and that the show recreates itself every three years.
While I here some people on here say that the adding on of the chacaters would take away the focus of teaching kids, I just saw the commercial with Oscar The Grouch and Maria eariler today, and Oscar said that one of the things that Sesame Street teaches kids is to respect the differences and opinions of others.
I'd also like to add that while America in no longer a melting pod, it is a mosaic. When it was a melting pot, a lot of ethnic people just simply blended in with the American way of life, where as now, people from other countries not only blend in with the way of life, but they are also able to keep and maintain the cultural Identity.