But as you say, it's ahistorical because by 500 AD you have lots of new nations arriving on the scene which aren't represented in PAE. I personally see no benefit to extending PAE further with the same civs, but then my PC won't take me much past 1AD so I never see the late game anyway. But an early medieaval game or scenario would for me include the Byzantines, Arabs, Bulgars, Franks, Goths, Mongols, etc. You still have the Persians but most of the other ancient empires are gone. And Rome would be split in two.