Reading Thom Hogan's report I too think that there will not be a follow up for Df.
When it came I was, as most were, alarmed at the price, although the D4 sensor gave it a little credence. So most thought of the Df as either an expensive D600 with retro look with a D4 sensor, or getting the D4 cheap and in a manageable package, less all the frills that I don't use.
Nostalgia got the better of me, so I bought one new, as a maybe I will like it camera and within a short time became the camera, putting the D800 into the dry cabinet almost for good - I have to continue to use the D800 for UW shooting as there is no underwater housing for the Df, and it is very expensive to replace the UW housing.
Since a year ago I bought a third party split-image screen and had almost never used AF lenses on my Df. I also acquired a D500 recently for birding, which I am using almost exclusively on a 300/4D AFS + TC-14EII.
If my Df dies it would be time to hunt for another in the used or NOS market. I am not holding my breath waiting for Df2. The rumored mirrorless, I will wait and see.