I haven't seen any indications that astronomy methods need to be applied on camera color profiling, I don't think that level of precision is required. Of what I've seen so far camera profiling is the most approximate among the typical profiling tasks (screen, print, camera). Still I've added stacking in the latest release so one can experiment. Of course it does not hurt to improve the quality of input data, but at some point it becomes overkill and one is doing more work than necessary. From the results I've seen so far flatfield is necessary if you lit the target with one lamp, but if you have a quality "copy" style setup flatfield is overkill. However how large measurement errors one can accept is also a matter of taste, so different users will come to different conclusions.
As a sanity check one can make one profile with "sloppy" measurements and one with all bells and whistles and compare the results. With DCamProf you can also make experiments with SSFs (where measurement errors are nil) and do some noise-adding experiments and see how things start to deviate.
About the D50 whitepoint, the reason FM is D50 is that profile connection space is D50, to be able to get further in the color pipeline we need to get into D50. However, it doesn't necessarily mean that FM must render the color as if the target was lit by D50, you can keep the color appearance of the original illuminant if you want to. If you want to do that depends on the situation of course, if you're making a reproduction profile for Tungsten lights you probably want to make the subject look like it was shot under D50 anyway as it's better for copy applications. If you want to retain the look of Tungsten, to make colors look as they look to the eye under Tungsten, you need to do something else though. This is what the "corresponding color sets" experiments is about which CAT02 is based on. As said I need more data on the quality of its results though before I'll make it the default behavior in DCamProf.
It seems like you are interpreting the FM as it should be lit for D50 as well, that is the camera raw RGB values should be for D50 even if the profile is a StdA. This is not how DCamProf does it currently, RGB values are always for the calibration illuminant. Citing the DNG Spec:
"The use of the forward matrix tags is recommended for two reasons. First, it allows the camera profile creator to control the chromatic adaptation algorithm used to convert between the calibration illuminant and D50. Second, it causes the white bala
nce adjustment (if the user white balance does not match the calibration illuminant) to be done by scaling the camera coordinates rather than by adapting the resulting XYZ values, which has been found to work better in extreme cases."
I've interpreted this like the intention is that RGB values should stem from the calibration illuminant, and how the D50 XYZ values are derived is up to the profile designer ("control the CAT"), that is one can for example choose to re-generate from spectra for a copy profile, or use CAT02 to better preserve actual color appearance.
If we make the FM matrix based on D50 RGB values this means that the matrix will look exactly the same regardless of calibration illuminant, and that does not seem right to me.