While the D5 sensor is likely, I'd rather a Df2 with higher DR than with more speed.
I'm sure the D5 sensor could be tuned for higher DR at lower ISO settings if a slower read-out speed is used. In a similar way the designers at Nikon managed to get better performance out of the D4 sensor in the Df by accepting a slower frame-rate.
3: no screw-drive AF
I was actually a bit surprised the Df supported screw-drive AF, as I felt the camera was geared towards manual focusing. Removing the AF motor would allow the camera body to be smaller and lighter (which is not always a good thing). Of course AF-S would still be supported. But it seems the Df was designed for maximum compatibility with ALL lenses - pre-AI, AI, AF, AF-S, D, G, E etc etc, which appears to have been a good decision.
4: D750 class AF module
At very least!
7: STOP-DOWN METERING
Better support for pre-AI lenses would be useful, the current metering seems a bit clumsy. Either stop-down metering in some form, or add a prong to engage the "rabbit-ears" on pre-AI lenses.
1: no rear LCD (fine-tune done in tethered computer)
8: smaller or thinner
Removing the rear LCD would allow the camera to be thinner - consider the thickness of the D5500 or D750 body with the LCD flipped out the way...
I don't think this is likely though, being able to review pictures on the spot is just too useful!
What about a removable LCD? You can either plug it in and use it like the D750, or take it off completely...?
Probably a better grip and more sensible placement of the card door would be useful improvements.