Recently (last few hours) merged to master is Aurelien’s latest enhancement of the filmic rgb module. Since I (seldom) build darktable, I have been salivating with the hope of updating to master and finding this merged.
The ability to visualise the mapping on the graph and understand better the effects of the sliders is, for me, a game-changer. Very nice work, Aurelien. Thank you for educating me!!! 
For those on github, the full detail is here
