Without knowing anything about scripting:
I love the idea, but there will be much more work needed then "just" getting the script to work to make it playabe.
as in one of the first posts stated, elven factions might get problems with their low population (althought i always have highest population of all on my lorien-campaigns at around turn 100 with 2 cities...), so they would need much less units per troop, but better trained.
this will need some really good balancing, especially on their archers. else a troop of snagas might kill an elite elven troop, just because they don't have enaugh arrows in the air fast enaugh. this just shouldn't happen. so we need somewhat more damage and accuracy on them, or even faster shooting (is that possible without destroying the animation?).
but the real problem will be the orc factions.
first, they don't multiply like orcs. that's fine as long as the game works like now, but if you recruit just 4 troops of snagas you might empty most orc towns. and without much higher growth rates they won't recover from it, especially not the AI.
Also, troll count as "heavy infantry"... but having only 12 units, not 250 like most other orcs. so "unit class" won't work for them.
And: somewhere in the script you have to check for the faction, can't see it until now. but maybe i just don't understand enaugh of it.
either this, or all infantry and missile would have to count as 250.
for in orc armies, everybody hold a "weapon", while in human armies they have supply waggons and all those people who travel behind the army... even more for elite, so that's ok.
(well, 225 supporter for 25 bodyguard cavallery seems a bit... extrem)
but trolls? 238 people for... food? o.0
also, i don't think an elven army has such a big baggage. they are naturelovers after all, stamp with thousand feet and there is no more nature.
also can't imagine elrond going to a "courtesan" after battle... sure, some smiths and so on, but due to their quality of equipment even less. elven swords are cose to indestructable, at least against those wooden orc shields
sorry for some inappropriate english.... but i think the thoughts are somewhat clear.
I really like the idea, and in combination with the dynamic garrison script somewhere else here it would make population a really war-deciding thing.
don't think the AI will get it right, but must be awsome for multiplayer.