Hi there,
with previous versions of filmic I rarely used the preserve chrominance option, because I didn’t like what it does with the colours. However, with V4 I get better results, but often find the highlights to be oversaturated while shadows look well. Without preserve chrominance the highlights look well, but shadows are far to saturated.
I fiddled around with the midtone saturation slider in filmic and the colour balance module, but didn’t find a satisfying setting. This leaves me with the thought, that an option where chrominance preservation only affects shadows would be great. Do I miss something and there’s another option besides changing the saturation of the highlights or shadows with another module?