Is it ok to ask a 'plot element' question? Something such as, "Are there any sci-fi books where a future Earth uses the gold standard'?
No, this is still a variant on the 'open-ended list question' that the site frowns upon. You're basically inviting people to post examples of a trope.
Not all questions have a home on Stack Exchange. Please note the following types of questions are off-topic here:
Questions calling for a list of works, authors, …: What are all the books that have X? Who wrote about topic Y?
Trying to turn it into a mock yes/no question by replacing "What are all the books that have X?" with "Are there any books that have X?" doesn't stop it being a list question, it just means that you're sneaky.