Do you also have triarii units? I guess that could be useful not to just lose spearmen.

The game does have "ruins" in many scenarios, which provide stone. The problem would be to take care of a more seamless transition between all kinds of buildings and their corresponding ruins. Maybe later on all these concepts could be unified in a coherent framework, but right now unbuilding/unproducing seems the simplest way.   The game already includes Loot from killed units. Realistically, to the victor should belong the spoils, but as you say, in a game like this it's hard to determine when a battle ends, thus individual opportunism is what's accounted for.

I would find it "logistically" more "realistic" and tactically more "interesting" if destroyed buildings, no matter if self-destructed the enemy's, would turn into "mines" containing the resources which have to be explicitly gathered and brought to one's storehouses. Also a battlefield could turn into "mines" with the "loot", like scouring the field after the battle looking for usable stuff, although it's hard to determine when a battle "ends". Would change balancing heavily against rushers/attackers in far away foreign territory though. Instead of "mines", the resources could also turn into those bonus-/treasure-item-like things, although those don't have to be brought to one's storehouses.  

You could check out what we did with  <SpecificName>Hastātus</SpecificName> for rome.  My understanding is early on they were similar to hoplites in kits and then they evolved into swordsmen.  So in p1 Hastatus = spearman and then it is replaced in p2 by Hastatus = swordsman infantry_swordsman_b.xml infantry_spearman_b.xml

Well the game already does it for "hoplites" they have a mixin that allows all hoplites to have phalanx formation.   <Identity>     <Classes datatype="tokens">Hoplite</Classes>       <Tooltip>Hoplites can use phalanx formation</Tooltip>       <History>Hoplites were the very symbol of Hellenic prestige and citizenship, armed with a spear and a large round bronze-coated shield known as an aspis. Armor was heavy, with bronze helmets and a cuirass of either bronze or linen, in addition to greaves. Hoplites fought in a tight formation called a phalanx, guarding each other with their shields while they attacked the enemy with their 2.5 meter spear or short iron sword.</History>      </Identity> just add a visable class     <Identity>     <VisibleClasses datatype="tokens">Athenian</VisibleClasses>     <Tooltip>A true citizen of Athens.</Tooltip>   </Identity>