Well, the immediate initial test failed for me: I thought, "why not apply this on one of my own sites, where I have a sort of journal of poetry I've written?"...and there's no category for "Poem", and the request to add Poem as a type [1] is at least 9 years old, links to an even older issue in an unreadable issue tracker without any resolution (and seemingly without much effort to resolve it), and then dies off without having accomplished anything.
[1] https://github.com/schemaorg/suggestions-questions-brainstor...