@Krajzen I get your frustration, but I think you kind of made your own point: there really was no significant Persian state in Iran proper between the fall of the Sassanians in 651 and the rise of the Safavids in 1501. At any rate, I would like to see an Islamic
and Zoroastrian Persia if we could--and Zoroastrian Persia by definition means Sassanid since the Arsacids were pagan and the bulk of the evidence suggests the Achaemenids were, too.
Two Persias in the same time wouldn't make sense, because there actually were many sorts of 'nationalist' continuity, consciousness and identity that made Islamic Persians consider Sasanians to be "our glorious ancestors" and "old Persia". It would be logically equivalent to separating Hindu - Buddhist Indonesian civilization from Islamic one, the same thing happens here; religion changed, but continuity of identity, culture and language didn't.
Maybe unless second "Persia" was Samanid empire, which elite also considered themselves Persian inheritors of Sasanian cultural heritage, but at least it ruled over Central Asia far from modern Iranian borders, largely populated by "not exactly" ethnic Persian people speaking "not exactly" Persian language; it would be a grey zone case similar to Rome/Byzantium dispute, where main ethnic group still considered themselves Romans/Persians, but there are so many differences in every aspect that games like this separate them anyway, to the joy of many.
Samanid empire would also be the second best way to finally introduce Central Asia to the game, besides Timurids:
Now I have realized I have actually proposed arguments both for and against two Persias...