Professionals want digital cameras with two memory card slots so they can create an instant backup while shooting, just in case a memory card fails. For professionals shooting events or spending an entire day shooting in remote locations, the loss of a memory card is catastrophic. Unfortunately, the new Nikon Z cameras lack a second memory slot and the pros commenting on the linked article, below, say that this oversight by Nikon is a deal killer for professionals.
If you are not a professional and do not need a second card slot, the cameras do look pretty cool.