As obvious by the title, I think the morale meter from Red Orchestra 2 would be a great feature. I highly doubt, for example, you wouldn't blink an eye at 20 men in your company suddenly falling. Flanks could actually mean more than just the enemy having to turn around, cavalry charges become more viable, and it would help for realism and also encourage tactical thinking while not affecting the game much.
Not to mention the morale loss when your officer is hit; no more commanding from the grave, at least without penalty!