Really don't have a lot of time right now, but some further conversational bullet points before I disappear without ability to meaningfully respond at length to anyone for a good long stretch.
Christianity as we know it has that thing, that BC thing, which if we go by that, the Cult of Sigmar has been going on for longer than that by a couple hundred years. Islam is generally regarded as having a 7th Century origin point.
Sigmar is older than both of those. Ulric, Taal, Rhya, Morr, etc. are older than Sigmar. Myrmidia was a Goddess who became mortal and then re-became a Goddess, as far as most regard that whole situation, while Sigmar was a mortal who became a God. He was not a Jesus expy, he was explicitly and purposefully a mortal who later became a God. Their Cults have been running around doing things for a long, long time. There is Judaism, which is older more or less depending on what theological scholarly stuff you apply, but that's not the point.
The point is that they have had their holy works and texts and what not, and have had them, and have percolated them around for a long, long time as well. You will simply not find people who are ignorant as to the Gods, for the most part. How they regard them can differ wildly, but they're hardly utterly uneducated as to the Gods.
Furthermore, you're very unlikely to have a quasi sort of Islamic Golden Age of sciences and what not if you're just focusing on the Cult of Ulric and Cult of Sigmar i.e. the two biggest main Cults in all the Empire. Ulric, while not to the extent of Taal, has a good shade of anti-intellectual bent to the Cult, like refusing black powder for the truly faithful and also straight up refusing to wear helmets most of the time.
Having someone wander up to an Ulrican, pushing their glasses up their nose, and say 'Um, ackshually, I a mere common man have been properly educated and statistics show that cranial injuries blah blah lbah' at which point the Ulrican beats their head in. Because Ulrican stuff abhors trickery, and any tactics that seem cowardly, and solve their disputes often with active martial combat. You are not going to convince Ulricans that they are wrong, a lot of the time, simply with words and such.
Meanwhile, Sigmar has the very first in their list of major tenets as 'Obey your orders', another about dwarfs, another about opposing greenskins+Chaos+corrupt magics, and also 'Work to promote the unity of the Empire, even at the cost of individual liberty.' and 'Bear true allegiance to His Imperial Majesty, the Emperor.'
So on the one hand, there may well be a market for printing out Sigmar books. And maybe only Sigmarite books. And maybe you trying to print things that disagree with Sigmar means you should be burned at the stake, and your tainted printing press too. Opening up options and opportunities can be a great thing, but it can also lead to people questioning or grasping for more and even if they are capable of doing so and may even be right to do so there lies the major issues of doctrinal friction. It might work out for the better, it might not. The point is, it's not that simple.
I've brought this up before, a bit hesitantly, but we just can't necessarily equate IRL religious stuff with IC Warhammer religious stuff. Whatever your beliefs on faith healing and miracles and what not, the simple fact of the matter is that Warhammer religions do faith healing and miracles - and they do it a heck of a lot more with a lot more in-universe documentation and proof and 1st hand accounts than they have ever taken place IRL. Vast armies of actual infidels and daemons straight up do just come out of nowhere and attack sometimes, instead of just calling opposing people IRL such things. The Pope has called Crusades, but I've never seen nor heard of the man calling down a massive cross-shaped meteor to slam into the earth and break apart the walls of a castle made of blood and bone which manifested out of a battlefield full of freshly slain dead that was staffed by straight up demons. The way of regarding and treating with religions between IRL and IC cannot be a 1:1 ratio, it just can't. When a Taalite priest tries to show a machine-made book to the gargantuan super moose with green glowing eyes and ivy-covered horns in his dreams and Taal says 'nope, don't like that' and the priest wakes up with the machine-made book rotted away into mulch by his bedside. When a Verenan prays so hard that the pages of the books they've nailed into their skin start glowing and forming a large translucent shield. When a sneaky Chaos cultist sneaks in a regular seeming book on the outside into a library and some bored scholar grabs it and doesn't even notice that with every word he reads aloud to his children that their souls are draining out of them and into the book.
I'm not saying that these things are omnipresent and constantly happening or are constantly going to happen, just that they can, have, and do on a level that requires active mental separation from how one regards IRL and Mallus and Warhammer as a universe. Which means that they have to be treated with somewhat of a different mentality. In the USA, we still take our shoes off and all the what have you, despite 9/11 being a ways back, and there being very few - comparatively - plane hijackings IRL, we have all sorts of security measures for these few things that happened those few times, and a lot of pushback on culling those measures. Horrible tragedies and mistakes, but you have to remember that such things happen in Warhammer society - comparatively - a lot more. On Mallus, witches do go crazy and call down demons, necromancers are waking up graveyards or making horrible frankensteins, innocent children are corrupted for no good reason and at no fault of their own sometimes even in the womb, and people make mistakes that can damn themselves or others even with the best of intentions. Ignorance is sometimes a defense against the horrors of Mallus, and yet sometimes they are a terrible vulnerability! Same goes for education and the educated. Sometimes the smarter people know better, and sometimes they think they do, but they don't.
And using the Bible and the Quran as examples as two mega big religions, just like Sigmar and Ulric, just doesn't work the same. Because they don't want or go about things the same way as God/Allah/Whatever.
Which is why, at the beginning, I specifically brought up Myrmidia and Verena.
Because those are the Gods that believe in enlightening people through their teachings which come with literature, education, instruction, questioning literally baked into their Cults. It is a standing issue between Myrmidians and Verenans and Ulricans/Sigmarites that the former are expected to question their teachers and priestly instructors, to debate them, to engage intellectually, whereas the latter's response is a hefty beating or lashing or whatever instead.
If you want to push education in the vein of religious boosting as mentioned with the Bible and Quran with the printing press, you go with the Cults I already mentioned. Who, however, it needs to be remembered, are a minority amongst the other Cults for a variety of reasons, and that have had a lot of pushback from Sigmar, Ulric, Taal+Rhya, who have a weightier grasp over the people by dint of massive historical and cultural weight and inertia. You could try with the Cult of Sigmar or Ulric, but there are the difficulties involved, the actual doctrinal issues involved, etc. but of the Cults, the ones that would actually support and engage in the same sort of manner as seemingly described/desired with boosting literacy with the Bible/Quran would be - again - Myrmidia and Verena.
Also, yes, ink and actual paper are expensive.
