Yes, I now have this - the auto-apply bit is set to scene-refered (AgX), so WB is by default set to as shot to reference, my style then disables the AgX module, switches from the default color correction scene refered to D50 illuminant, applies an auto exposure, adds a few tweaks and mainly - works for every camera. This is a solution that works for me, but, and I will repeat myself, still doesnt explain why the WB saves the way it does 
Have you tried the specktrafilm module port to darktable… I have lost track of the development there and what may or may not be missing but I think it did have most of the features and at least in some cases would negate the need for an export…thought its only in development and not merged yet…
Yeah, I run the experimental branch of python spektrafilm which has some features not yet ready for “main” branch of spektrafilm, let alone the module. But thanks!
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Funny thing, the color calibration tool has the same upside-down saving mechanism. The default “same as pipeline” setting saved as a preset works, because the illuminant temperature is identical between all cameras (since it doesnt need to do any transformation), but once you switch your illuminant to lets say daylight and save… Well, youre back in the same territory as with the WB module - since here it saves the CCT kelvin value, which is profiled and different between cameras, instead of saving the selected illuminant setting 
Well I filed it as a bug, this behavior is ridiculous and infuriating