In APS-C I would go for Fuji. Their lenses are fantastic. I especially liked the X-T1 with the 16,23, 35, and 56mm prime lenses. These are clearly targeted to photographers and do have some smart features. For macro the 60mm is incredibly sharp, but painfully slow (the Zeiss 50mm is a better option). I added the X100T to have a one camera- one lens solution. My main issue with the X100T was that I could not comfortably hold it. Camera-size is fine but lens was too small for me (I like to use my left hand to support/hold the lens). The 23mm Fuji lens worked better for me. I also looked at Sony but the Fuji is - in my opinion - more a photographer's tool that is fun to use. Esp. the X-T1 with its dials for ISO, shutter speed and Aperture. But also the implementation of the priority functions. Nevertheless, last year september I decided to sell my entire Fuji set. I did not like the slow AF (much improved in the X-T2) and I had to constantly correct colours in LR when I processed raw files. Jpegs were fine (in fact, I only used jpeg with my X100T). Another thing I missed was the intangible "3D pop" and the clarity of full frame sensors with bigger pixels. Therefore I switched to the D750, although I also considered the Df.
In your case, I may consider sticking to the Df with some light(er) lenses. It's the weight of the lenses that make the difference, not the camera. Just take an X-T1/X-T2 (with the 16-55, 50-140, and 100-400 lenses with you. Your back won't like it. I decided to opt for the D750 with light(er)weight lenses: 24mm 1.8G, 58mm, 70-200 f4, and 300mm PF f4. The only exception is my 35mm lens: a sigma art 1.4. But I am about to add a lightweight nikon alternative for travel.
More recently, I thought about adding a lightweight alternative, including the X-T2 (or x-pro2) but concluded that the D750 with 3 lightweight f1.8/4 lenses works equally well.
There are two mirrorless cameras that Iremain interested in (besides the upcoming medium-format Fuji): the Leica Q and Sony RX1 (ii). Excellent size and wonderful output. IMHO, a fullframe mirrorless camera does not make a lot of sense if you add fast lenses (or converters) because it won't save you noticeable weight. I also thought about the Df but the D750 is about the same size and weight. Maybe the Df successor will convince me. So for now, my travel camera is the D750.