I also remember that barbarians used to be unable to read scrolls, but now they seem to be able to, and nothing is mentioned on the changelog.
That sounds like an ADoM thing? Beastfighters and barbarians there are special-cased to not start with Literacy even if they have the Le requirement. (I think that one gets overridden by elves always having Literacy, if you're running a frail warlord with delicate sensibilities for some reason...)
I'm pretty sure the PC in Nethack is always assumed to be literate (even if the player refuses to let them read anything else for the conduct) because it's mandatory to read The Book to finish the game. (Side thought: What happens if you attempt to read it while blind or polymorphed into something eyeless? If it works, that means going through the motions of reading is enough, allowing for a truly illiterate chacter...)
Reading conduct-breaking items while blind still breaks conduct. Reading the book of the dead, blind or otherwise, does not, since otherwise you couldn't beat the game.
I'm not referring to the gameplay conduct; I mean it more as a conceptual thing: If the Book of the Dead functions while you physically can't read it, that would imply that the in-universe functionality of the book isn't based on literally reading it, allowing for somebody that
is, in-universe illiterate.