Fair enough. That was a spur-of-the-moment thought. To be honest, this
proposal is a massive generalization from, ultimately, a single
use-case.

And this should make it easier for third-party code to be functional
without even being aware of the Path object. There are two basic
things that code will be doing with paths: passing them unchanged to
standard library functions (eg open()), and combining them with
strings. The first will work by definition; the second will if paths
can implicitly upcast to strings.