This is just my opinion and it has nothing to do with facts or research. There is no reason why guitars should have a nut made out of bone of something softer than any other frets. Nut pieces wear and tear over time. If you change string gauge, you have to make a new nut.
This is not the case with zero fret:
What I do is use stainless steel jumbo frets as guitar nuts. They are really hard, so hard that I don't use them as regular frets since my tools can't handle them. If all other frets are installed right, the zero fret works as long as you have something to guide strings.
What I did I carved small grooves to strings. I know that there is a chance that the strings will carve more wood from fretboard but since they go straight, I don't see that happening any time soon.
What do you think?
Comment and share your opinion!