Hello!
The latest Book mod looks really great, and it made me to think about a religion mod (since there may be some related mechanics). There is Religions of Rimworld, but it is half-broken and developed very slowly.

By the way, you could also make a music mod. There are two nice mods: Musical Instruments with great models and mechanics and TribalInstruments with sound :) Would be great to have a mod with both advantages!