That's far from simple. You can't just add a border that ends in nothingness, and no event at all to model the neighboring countries. Before the map expansions, the Mongols were represented by event troops spawned on the border of the map, etc. You can't just "disable and add white fog", because if you do that, you need to add something else to represent interactions with the disabled regions, or to completely re-balance the game.
Imagine disabling byzantine empire and doing nothing more? The Arabian Empire would just conquer the world without any hassle.
they should actually have done it for India - Just a white space as if unknown land. I think it will pop up eventually - otherwise mongols is just incomplete experience.
