I'd love to be able to write a book in game. Or rather, my characters would love to be able to write a journal.
Helena has more than once told me she'd love it if she could write her journal, rather than getting me to do it.
Helena should've stayed in school.
I'd love at least a note system, so that I could attach typed notes to a quest's journal entry to fill the inevitable information void. Notes for the world map would be cool too, so that I could note which dungeons hold what kind of enemy. Console users could get a list of prewritten notes to attach like the names of locations or mob types, or can type it with a virtual keyboard if they're feeling particularly masochistic.