I think after Rome they should go back and revisit Dark Age/Medieval Times/Renaissance (800-1600 say) with the Rome engine. I feel the Medieval times deserved the ultimate warfare treatment. This time though they have a map of the known world, from Ireland to Japan and Finland to mid-Africa. That way you could have the Mongols sweeping across Asia and Europe, or maybe creating your own European Shogun Empire. This time though it could have elephants too, realistic castle sieges and naval warfare. And in 1492, the New World is added to the map, and the fearsome Native warriors of the region (aztecs, mayas, incas) are encountered, as are the Conquistadors. This would make an awesome game.