Thanks for the quick answer!
Hm I guess I could try to contact the publisher. They do say in their business statement that they are all about learning, so maybe they’ll be open to the idea. At the same time, I’m always horribly self conscious about my Japanese when I write something formal, so I might take an infinite amount of time writing that email.
At the same time, @Candygaming gave a good suggestion: as long as people have the poem, some explanation, and historical pointers, they are good to go.
All that can be found in the public domain so I can just post those things instead. At the same time, people with the book will be able to also discuss the text as usual for a book club.
… Just to be sure, is the nomination post fine? (I copied it in the OP; see “Pictures”) if not… I don’t know what is going to happen to the book clubs… so actually don’t answer that maybe?