Years ago, Nikon tried something really courageous with the Nikon Df–but if the company were to create a brand new Nikon Mirrorless Full Frame F Mount camera, it would be an announcement that would genuinely shake up the industry. If any camera company were able to do it, it would easily be Nikon or Pentax due to the fact that they’ve been using the same mount for many, many years now.
Canon used the FD mount for a while and then almost lost everything when they switched to EF. Nikon has used the F mount for years and has made it evolve over time with some lenses having autofocus abilities and some not. The Pentax K mount has done something similar over time. Years ago, Pentax made a mirrorless K mount camera which arguably could have been made smaller just like many of their other film SLR cameras. Nikon, for many years, also made small, professional quality film SLR cameras like the iconic Nikon FM2. With the Nikon Df, the company created a nod to their history and to the folks that wanted a retro-style camera. But it was, and still is, physically large. In fact, it’s not much different from the company’s other full frame DSLR cameras.