Imagine if LOTR was on github...

I like the idea of modularization in fiction. This already happens in fan fiction, but you have to extract most of the parts yourself (I think?)

It would be really useful in SF/Fantasy novels where you have to build out lots of worlds, characters and miscellaneous details like languages, landscapes and history.

If you could "borrow" a lot of the structures that are in a Creative Commons license and use them in your story, you could focus on the parts that are important to you, and let others focus on what works for them.

Artists could come in, draw characters. Cartographers could make maps. App developers could make interactive features. Linguists could make fictional languages.