Any interest in a "film negative" feature in RT ?

Software RawTherapee
90

Or easier, assuming you already cloned or ran the build-rawtherapee script in the past:

cd ~/programs/code-rawtherapee/
git checkout dev
git pull
git checkout -b rom9-filmneg_stable_mults dev
git pull https://github.com/rom9/RawTherapee.git filmneg_stable_mults
<it will ask to merge, commit the merge>
./tools/build-rawtherapee -b