Yeah, the color shift is the biggest problem, otherwise Darktables Equalizer is already fairly good. If the would allow chroma control on the residual it would work much better I think.
I gave it a quick whack in Gimp with the Wavelet-Decompose plugin and a simple mask based on similarity to the haze color.
(left is the raw as I exported it from DT, right is dehazed in gimp with some simple masking at the sky and around the trees mostly because there was some fugly haloing caused by the non edge-avoiding wavelets the plugin presumably uses).
IMO the lighroom results still look the best - and that with a simple slider. 
it would be really interesting to try to do something a bit more advanced with darktables edge optimized wavelets. But I guess it would be sufficiently painful to extract that code into something usable outside of darktable. 
Gave it another whack, trying to fake what would happen if you could remove the residual in darktables equalizer:
This time at a slightly less extreme setting.