This is the biggest thing for me. Please give me Assyrian/Sogdian/Khwarwzmian and Nestorian/Manichaean content (I know Zoroastrian is an almost inevitability).
Rather than them pulling a super irrelevant religion out of a hat like Basque paganism, I’d rather them focus on strengthening the things that already are.
Make a Manichaean Persia as interesting as I’m sure a Zoroastrian one will be. Give Assyrians appropriate art and make playing an independent Assyrian ruler interesting in a way that isn’t just Bronze age LARP. Let me BECOME Prester John, an ally of Christianity from the East against the Muslims.