Newly developed high-resolution stacked FX sensor. Three different sensors were tested: 45-46MP, 50MP, and 60MP. My guess is that they will go with the 60MP or the 50MP version but I could be wrong (the Z II already has a 45MP sensor, there is no need for another camera with the same resolution). I have received the most tips for a 50MP sensor based on what's inside the new Sony a1 but improved and with even better performance.
New EXPEED processor designed for 8k (newly developed Imaging Pipeline Processor to broaden sensor readout emphasizing speed)
Improved AF (Object detection AF)
"Stunning" AF tracking (better than the D6)
Two XQD/CFX type B memory card slots
ISO 64 - 25,600, Hi1, Hi2
Improved noise levels and specifically significantly better dynamic range
High resolution, blackout-free EVF: probably 5.76 MP or maybe even 9k MP viewfinder, 120 Hz refresh rate (the resolution can be reduced to increase the refresh rate)
New user interface (no second LCD screen on the back like the D6)