OP here, you're right and it's even worse than you say. After my brief literature review I'm starting to suspect that the entire problem of demosaicing is ill-p

OP here, you're right and it's even worse than you say. After my brief literature review I'm starting to suspect that the entire problem of demosaicing is ill-posed in most of the ways it is studied (certainly including this little side project). Some of the survey papers I saw talk about this. The color image pipeline is basically ignored in all the analysis I've seen, and to the best of my knowledge the common assumptions are based on dubious heuristics. On the other hand it works well enough...