So we both do not have particular use cases in mind. But I also have a stomach feeling that this may be useful for end-users sometimes. Especially if we get them for free, because we use them internally. I was just interested if you had cases in mind.

We still don't know the future of white-box macros, but regardless I like the type-safe Nat implementation better. It makes it more implicit in user code what is type-safe and what is not.