"Medieval" by definition refers to the Middle Ages: "The period in European history between antiquity and the Renaissance, often dated from a.d. 476 to 1453." [source] We can squabble over just how wide a swath, geographically, this refers to, but generally speaking this does not include East Asia, South and Central Africa, Australia, or the Americas.
As I said in the other thread, during the Middle Ages (the 5th century to 15th century), Europe was in the process of being Christianized; so-called pagan beliefs still existed in many places at various points throughout the medieval period, though most of these had disappeared by the end of it. The most well-known of these would probably be Norse paganism. As has been said by others, Islam also posed a significant threat to the dominance of Christianity, and Judaism was also present in small but significant amounts. I personally have no problem whatsoever with these types of religions on Dwilight. Other religions and mystical systems making an appearance at this time were gnosticism, Zoroastrianism, Catharism, and alchemy, though some of these were secret and others were present only among the intellectual elite.
Furthermore, as I also said in the other thread, if SMA is going to be strictly enforced on Dwilight, I will expect those ill-thought-out and truly quite terrible region names to be changed. (Personally, I'd also like to see region names fixed to include apostrophes if they're supposed to have apostrophes.)
Finally, the last thing I have to say about Serious Medieval Atmosphere is this: most monarchs, knights, and nobles were not literate [source]. In fact, Frederick II of Sicily was notable because he could read and speak six different languages. So -- how serious do you want your medieval atmosphere?
You miss the point of SMA I think. It is not suppose to truly replicate the exact circumstances of the medieval period. It is suppose to provide for a fantasy setting that has the feeling and atmosphere of the period. At is most crude the SMA was suppose to stop things like religions worshipping doughnuts. SMA to me has always been less about enforcing a particular setting, and more about encouraging and enforcing behaviours by our characters that would make sense in the context of being "noble"
