The tone curve can be set up on the computer using the Nikon Picture Control Editor(PC software) then uploaded to the Nikon camera.
Unless you were exporting direct from the camera, I don't see that loading a custom tone curve into the camera is an advance over using the same tone curve in a pre-set in the computer. Sure, Nikon could have offered a choice of pre-set tone curves - "no shadow clipping", "high contrast" etc which would have reduced but not eliminated the problem.
The reaction to the D850 negative conversion tool is being driven by people - like the reviewer in the original link - who are already scanning negatives with a RAW workflow, who find the D850 negative conversion tool does not meet their needs. But instead of saying that Nikon botched the tool because it does not do what people who are already scanning negatives want, what if we try to make sense of Nikon's choices by asking who they
would work well for?
Nikon's choices would work well for people who have never scanned a negative in their lives, but have a whole lot of negatives in a box that they would like to get a look at, quickly and without a lot of work. They do not intend to make fine art prints, maybe just a book of old family photographs for their grandchildren. Old colour negatives will need a lot of post-processing to look good, but because the degree of fading and staining is so variable it is hard to see how the camera could do a better job, and the tool will allow you to see who or what is in the photograph and decide whether you want to take the trouble needed to make it look good - and yes, having a RAW + JPEG option for the negative conversion mode would save photographing some negatives twice - at the expense of massive files, most of which the intended user will
not post-process.
