Although Umatate has not said as much, there is no doubt that this future model would be a response to Sony's A9. In simple terms, Sony continues to shake up Nikon (and Canon, from elsewhere) in the market for mirrorless systems, or even interchangeable lens devices as a whole. A parallel to the D5 could prevent professional photographers from switching to Sony. And for Nikon, it's essential. Camera platform switches are expensive by nature (lenses are rarely cheap), and it could be a lot more expensive for Nikon to win back users.