I guess I'm in the same boat as Airy
I'm still loving my Df as a "no brainer" camera ! I guess that if I do progress in photography I might "need" a Z one day, but for now it fulfills all I need from it.
When I do the semestrial shots for my school of architecture (about 1500 shots per event) of various events, expositions, jury results, famed visitors for conferences, it goes easily on one battery (though I have one more, just in case). All that in not so good light and mixed lighting...
Most of those pictures are either for the web site or for prints (school schedules, leaflets, year books, etc.). While I'm not shooting by the hip, I need to be quick to capture a position, an emotion. The Df's simplicity allows it, and the files are great !
It's small enough, and surprisingly my best shots are with MF AI-s lenses, even though I now wear glasses for reading or computer work. For practical purposes, I often use the G lenses or zoom (as the 24-120mm f/4). I recently bought, second hand, the 60mm Micro AFS-G, and it's becoming one of my favorite (between 50mm and 85mm).
So I'm not parting with the Df... Yet