Just had an idea for the new MTW, don't know if anybody suggested this.

Let's make the archers upgradeable to an armor piercing variant. I mean, we all know that AP versions of arrowheads existed, why not put it in the game also.
Maybe we could make them appear "chronologicaly" after different versions of armor appear (and light and heavy crossbow variants also) to better illustrate the historical quest for the best armor penetrating solution in ranged warfare...