Steve Perry wrote:
I think it would be doable, but I wouldn't hold my breath. With very few exceptions, Nikon does not add features to their cameras via firmware updates. Plus, Focus Stacking is a nice selling point for the D850, if they added it to the D810, that would just be one more reason to keep the D810 and not upgrade. If anything, I might expect it to be added to the D500 or D5 (D5 most likely).
I agree with you, Steve. The FB tube is just an extension tube with the stacking computer chip inside. If they updated the 810, I would do exactly what you just stated. The only features that make the 850 attractive to me are the 9fps, and the articulating screen.