In the 1200s the Catholics and the Orthodox were really interested in converting the Mongols. (If I remember correctly, missionaries actually met Batu Khan and threatened him with fires of hell. Batu responded by saying they were his guests and sought to convert him, so threats weren't the best way to proceed.) In the end, the Muslims were more successful, but retrospectively it could have been entirely possible to have a Christian Golden Horde.
Will the game represent this? Shall there be an event chain for example? Or is it only the matter of a child catching the province's religion or something?
That would be a really cool thing to be represented in the game!