Pictures courtesy of Nestle Japan
My research would indicate this is old stuff... unless it is new stuff. When I tried to find any reference to gold bars shaped like KitKats, I found news articles from 2008 about a campaign in the Middle East in which consumers of KitKats had the chance to win real gold bars. However, the answer that was eventually revealed was far less interesting.
Apparently, they were teasing people by showing a portion of something as boring as a marketing award for the best team worldwide that works for Nestle. For 2012, the Japanese team had been given this award, which is called the George Harris Marketing Excellence Award and it was, in large part, a response to the "adult sweetness" campaigns and redirecting their marketing toward adults in Japan. I'm sorry to say that it is not some sort of new and exotic flavor, but I will congratulate the Japanese team on pulling their brand out of the quagmire of bizarre flavor offerings and coming up with something that boosted sales.