Our in-house #Scheme dialect (SKILL++) makes heavy use of Disembodied Property Lists, an archaic feature of ancient Lisps like MacLisp and Franz Lisp.
They're an interesting data structure: a list-based associative data structure with unique identity and intended for destructive mutation.
I started drafting an SRFI. But I'm probably going to give up. I can't envision getting corporate VP-level approval for publication, and even if I do, I expect the SRFI commentariat to die laughing.