There is a magic power stopping me , from say crossing from Tashkent or Samarkand to China or Mongolia - two mountain ranges , namely , and a freaking huge desert. There's a magical power preventing me from easily sending an army down into India - the Hindu Kush mountains literally mean Hindu killer , by the way . Marching from Hormuz to Kutch in India would likely lead to the death of most of my army - just ask Alexander.
There's not much stopping me from marching armies into Persia , all the way into Transoxinia , geography wise save a huge load of space. If Khorasan is firmly under my control , Samarkand and Tashkent are within striking distance - rich , tempting loaded cities seating pretty on the Silk Road - even the Fergana Valley , which is probably a good place ( besides Kashgar on the edge of the Silk road) .
Irregardless though , even if Paradox does not include these regions , I'm quite certain that many mods will include these regions , if only for the purpose of simulating the Seljuks and the Mongol invasion better, and to give a real Challenge for a competent, adequately skillful and experienced Kingdom of Jerusalem , or Georgia player , or a Byzantine Empire that decides to conquer the Muslim world to do .
For a player playing as a Christian in Outremer , or as the Byzantines or an Armenian minor , or Georgia , adding more depth to the Muslim world ( province wise) would give them a far greater challenge , from a game play perspective . Let's face it . Read any successful Byzantine AAR. If the player choses to focus on the East , you can , if you want to , conquer Baghdad in about 100 years or slightly more game time ( and even much less if you are lucky enough , or good enough). If the map ends there , then what ? Whack a Muslim Spawn army and hunker down for the Mongols 100 years later? Turn your attention west? But include Persia , and include Transoxinia , which was very much considered an extension of Persia during this time period , and you still have a significant challenge . The challenge from the East wouldn't be truly over until you drive Islam out , not merely out of Persia , but also out of Transoxinia. While going west , you have to watch your back in the East and seriously pray that someone doesn't form Seljuk Mk2 before the Mongols.
You've defeated the Il Khantate , and forced a white peace as the Byzantines ? If , by 1220 plus , Persia is still not yours , you still have a Mongol menace seating at your border in Persia - and it ain't truly over until it collapses to bits , or you push it out of the edge of the map . If Transoxinia is added fully , the edge of the map will make sense . Right now , if I threw the Mongols out of Bukhara , and they're still receiving reinforcements from Samarkand ( check the CK Mongol event file - it's a real event ) , so close by , what's stopping me , from a role play perspective , from marching on to Samarkand , and putting the Tian Shan and Pamirs between me and those dammed Mongols?
From a historical perspective , it makes even more sense , since these places were culturally , economically , and very much politically as well as Militarily involved and PART of the Muslim world of the Near East , even to the shores of the Mediterranean . Yes , this is a game centered on Europe , but it also a game centered on Crusades . If the Muslims are nerfed in this game ( especially to the point of slicing of all of Persia) , why call this Crusaders King ? We might as well call it Europa Universalis : Medieval in the same vein as Europe Universalis: Rome.