The Mystery Magazine Online Murder, Mystery, and Mayhem. Some say, yes.
Genre fiction tends to be cyclical in nature.
But this time around, I think the mystery market shot itself in the foot, so to speak, and while not a life-threatening injury, considerable blood loss is to be expected. I think authors and publishers share a large portion of the blame. They were too eager to sell more books. Same as happened with the romance genre a few years earlier. Nearly every publisher expanded with new imprints, more titles, new authors and many encouraged their established authors to write more quickly, to get more books out.