Well, I see your point but I do not agree, lightmix is scene specific, yeah but tweaking lightmix without post settings is well not to handy, accurate, realistic or even sensible way to do things to say the least. Especially when all lights are set up closely to the manufacturers specifications (ies, power, temperature, light source size) and when one does a day render without them and night or evening or both with them on, without going wild with the lightmix sliders intensities - I, for instance, tend to use only two positions 0-1 which is well the only way to go if you want to get +- close to real results preserving realistic light power consistency across the different light sources (except if you're planning to use some dimmable light sources or dim the environment for the evening render but that's another matter). So in that semi-simulation case the post settings needs to be tweaked for each lighmix preset (group of lights) regardless of what one wants, of course one could achieve some results tweaking lighmix element intensities and colors but that is unintuitive way to do things for such tasks and not consistent with interior photography in different lighting conditions - white balance, exposure, and yeah non present in cameras but still very needed highlight compress, needs to be set up for each shot (or afterwards) if one does not rely on automatic camera settings, not to say different requirements for glare and bloom for each of those lighting conditions.
On the usefulness of Post presets across different scenes, well yeah that is the case but why not just simply ignore the lighmix settings saved from the scene where it was enabled when loading that preset to a different scene - either to the one not containing lightmix element at all (that would be the simplest) or the one containing different and differently named lightmix elements. Well those render elements are usually named differently across the scenes so I honestly don't see the problem with ignoring those which are not present in that scene and if there are the same named ones all the better (I could find a use for that too when using same light by the same manufacturers across the different scenes) - yeah I see the potential problem if people will accidentally leave some of them named by default but is that such a problem to fix that later after render and save the preset anew for that new scene ?
And about the frequency of use, well that depends on the scene - did some interior recently where each camera required up to 6 lightmix presets for different lighting conditions\scenarios evaluation by the client - so yeah it is easy to get lost in all of those saved configs - there were 12of them 6 for lightmix and 6 for post, each named to be recognizable as the part of the other one like "interior night top lights only LIGHTMIX.conf" accompanied by the "interior night top lights only POST.conf" and so on, thus I needed to load them twelve times for each render no to big of a chore but still could be made easier to manage if they could share both settings + when the both of configs have the same extension it's too easy to accidentally overwrite the saved post preset with lighmix's one and vice versa which can lead to lots of frustrations when the deadline is near and there's a couple of views to render.
If my chaotic writing still doesn't convince you what the shared presets are needed, then as a compromise I would suggest what at least the extensions of those configs should be made different - that would settle it for me, at least to some point ))
