I want to propose another sample image… 
Last week-end I went to the Alpago mountains in Italy, the humidity was quite high and so was the fog in the distance. I shot this picture of a paraglider with a very foggy background. I think this could be a nice test bench. I was inspired by some of the corrections suggested by @Jonas_Wagner.
Here what I applied with darktable:
- white balance corrections
- base curve and tone curve tweaking
- velvia and vibrance enhancements
- color zone tweaking to improve the greens in the lower part of the image
- equalizer to increase clarity
- denoise profiled (wavelet for chroma - non local means for luma)
darktable output (left) - in-camera jpeg with default settings (right)
What do you guys think? The colors recovered don’t fully convince me. Maybe I went to far with the saturation… Unfortunately I don’t have a Lightroom copy to compare its dehaze algorithm.
If you want to experiment with this image feel free to use the RAW file: https://drive.google.com/file/d/0B28JOPvq926IZllFTGlaS1VINk0/view?usp=sharing (updated).