in some aspects the Zf will be far better, and it will work better together witz Z-lenses and it will be better in adapting thirt party lenses, and it has the benefits of an electronic viewfinder and video functions
but it will never have the benefits of an optical viewfinder and even if an FTZ adapter with Ai support will ever see the light the Df will have better support of AI(-S) lenses and will benefit for not having Video options distracting from photography and has a control element for direct access to the exposure metering modes
Thus i will keep my Df and all options (even though the front wheel of the Df is looking nice but a real nuissance for good camera grip
I will never part from my Df but it is in semi-retirement now. Getting old, a rubber gasket (ISO wheel) needs replacement, aperture lever actuation replaced once in 2017 probably needs replacement again, some buttons on the back feel awkward... well, I'm ageing too, am I not? and the stiff and sharp-edged front wheel always hurt my fingers - well, most of the time I use AI lenses.
...and while I do not enjoy the Z6ii as a camera body, it delivers good results (precise focussing, stabiliser are important for my subjects). I nearly had a fit when it refused to actuate the flashlight, until I learnt (thanks internet) that flashlight and electronic shutter are not compatible. That saved the shooting session.
Still, I look forward to a camera I can enjoy, placing hopes in the Zf, in which case I'll resell the Z6ii. Next goodie would be a FTxyz with an aperture follower: little hope. I'll survive that.