Within the linked thread is a quote that the finish was so difficult to pull off that the cars that have it will be the only ones that have it. For what it's worth, I have the plated AEM7 and the matching Amfleets. They look really nice.
I recall asking Maury Kline about some of K-Line's plated cars at a Toy Fair open house many years ago. He also related how difficult the process was, something about having to plate the inside surface of the mold before each injection cycle, and how absurdly high the reject rate was as a result.
---PCJ