It's a real shame that they have done this, especially as Nikon are one of only two mainstream companies selling a 35mm film camera. The strength of a system is that you can use bodies and lenses interchangeably and a lens like the 105/F1.4 is crying out to be used on an F5 for F6.Yes, it forces you to buy a new camera and in the long run, it will help cut costs for Nikon but not for you. Also, it will remove one mechanical structure from the Mirrorless camera.
Besides that, they say that it will get better auto exposure during high-speed shooting and tracking.