Is anybody working on extending procdesc support to rfork?

The procdesc(4) interface is a Capsicum-friendly, race-free
alternative to fork and kill.  It's a good fit for a new feature going
into the Rust standard library.  However, it's not quite complete
enough to do a good job.  Is anybody working on extending it?  Or even
interested in doing so?

The functionality that Rust wants is:

* kill - we can use pdkill()
* wait - we can use poll() or select()
* spawn - we must use pdfork/exec .  posix_spawn would be better, but
we can't do such a thing without procdesc support in rfork.