I think that what is already in the library is relevent (good job, btw).
One might consider adding rituals, songs, biographies and more scientific works, or thesis. All of which can add substance and concrete tidbits to the setting of Yliakum. The bottom line is that information and folklore present in these works will most likely end up used in roleplay (if not implemented). As always, when is a subject fictitious, theoretical, based on innuendo or beliefs and when is a subject fact? There has to be a distinction between fact and fiction. Not to mention that what is 'fact' needs to be consistant.
You could perhaps mix song and ritual and give it a formal name like 'ablution' or 'solemnisation'. With each race or religion having their own versions (a vigil, praying, sacrifice, marriage, death, birth). A short historical journal detailing what major events that have occured in the known world might also be appropriate (a chronological record, ie: eclipses). Memoirs, Thanatopsis, liturgy, anecdote, legend, consuetude, habitude, praxis all come to mind. Again, some works are factual, others are fictitous (until proven otherwise).
While arts as entertainment would add realism, the covered topics would best serve the settings. So as far as what works might be written by Yliakum's citizens, i'ld suggest Essays and journals at least partly based on non-fiction.
Good writers: probably Londris because of the content. I guess that pretty well says what i'm thinking.