I think in the context of natural language for game worlds, "prose" is targeting the much lower bar of something that sounds like a human might write it, vs like "you PLACED KEY in THE LEFT DOOR. Proceed to A STAIRCASE" from games of yore. Understanding the much richer space of literary prose, such as the difference between the Shire and Westeros, seems like a harder problem, but also one that might be well suited for existing NLP training pipelines, because you can label a large amount of text with only a few descriptors. It might be tough to come to a consensus amongst literary experts what those descriptors should be, but e.g. if LOTR book 1 is "pastoral" and ASOIAF book 1 is "gritty", you've now got a lot of text associated to each of those labels. I wonder if anyone is working on this?