I spoke to S&W customer service today (on an unrelated matter) and the guy mentioned in passing they had discontinued the blue plastic cases in favor of old-style cardboard boxes. He told me guns were now being delivered in the new cardboard containers, however the M&P series pistols would still use black plastic cases.

I asked if S&W would now sell the empty cardboard boxes, since they currently sell replacement blue plastic cases for about $10 each. I was told they probably would in the future, but he didn't know when....perhaps after they sell all the remaining blue boxes.