Automatic battalion exist in other RTS , called Rise and Fall Cilization at War. That why I have the hope we can imitate that way. The game is freeware because Midway fall into a bankruptcy, but have a trickle to start to play.
Ptolemies, Seleucid and Mauryans are incomplete ( art department ) we haven't volunteer from main team specially our leader Enrique, need to review a lot of art concepts.
if another RTS had that feature and was one of top feature of that game, I think can work, I prefer create battalion from trained units a create , and when you need citizen soldiers , only disband battalion, and all are single again.
In AOE Slingers are good vs defensive structures but these rol was cover by skirmishes in AoK. ( I mean high resistance vs towers) -You forgot a special class like Maceman, it's like sword but with more crush attack and less pierce or cut. - Chariot it's another range cavalry but these in the old alphas aren't weak vs spearman - and a variant of Elephant are the ranged elephant... Many of this aren't in design document because nobody planned introduce the Mauryans.
For Mercenary camp and building like this you need an alternate type of capture. Similar to sheeps in AoK similar to Hesperides in AOM This last fits with the gameplay. If is surrounded by enemy or other troops its claimed by these units. Other examples are http://ageofempires.wikia.com/wiki/Plenty http://ageofempires.wikia.com/wiki/Healing_Spring
Many of that new features ever existed, but never in a claimed soul sucesor of AoE/ AoM. Citizen soldier is very similar to some Nordic units, that can fight and gathering resoruces. You can name a feature and probably there is a equivalent.