Short answer: GitHub - sadiedemight/i7-pronouns: Inform7 code for flexible handling of pronouns.
I did find an extension by Nerode, but it’s more limited than I hoped. I’ve got something that lets me add new pronouns for for output and for parsing, and I’m leveraging rulebooks for flexibility.
I’m still not entirely sure what’s the clearest way to encode a testable project in I7, so I did something a little backwards, with the testing code owning the extension itself as a resource.