I am not sure if the engine would allow this, but from a modders point of view I would love to see an option to actually be able to mod formations (e.g. make 19th century battle lines) as well as the option to mod the AI behaviour (e.g. have it use only certain formations, while ignoring others). It would also be awesome if there were actual horses incorporated, since at the moment trucks are used to pass as horses. These ideas are very probably less interesting for all WW2 settings but would open the door for new mods featuring other centuries.