Sounds really interesting!
What goes wrong when using nikon's NX with pixelshift?
I'll preface to say I tested this when it first came out but have not confirmed whether or not it was fixed in the last year.
It seemed like there was an off-by-one error in some of the maths that resulted in one or two color channels to be slightly rescaled compared to the third that introduced color halos on hard edges.
My app can detect when regions of the image are different between frames in excess of what would be expected due to noise and per-pixel variation and automatically avoid using multiple images there. That's something some cameras do in-camera but Nikon's software doesn't.
Last, for most lenses the aperture isn't precise and lighting is never perfectly constant. My app is the only one that does a precise exposure matching between frames before combining. Without that, you end up geting pattern noise across the entire image (checkerboard) that can easily reduce your dynamic range to 8-10 bits instead of the 12-14 you should get.
...and one more thing... my app is dramatically faster and outputs losslessly compressed DNGs using JPEGXL so the files are much smaller.
