I'm sure it's been suggested already, but please give us great control over troop assignments. We need it!
Allowing us to create groups and then assign individual soldiers to those groups would be a huge boon for veteran strategists and tacticians. Forming groups, then assigning them to commanders... Oh, now we're talking.
I'm thinking, create two squadrons of cavalry, assign them to aggressive commanders and task them with flank guard. Handpicked units so that both commanders have a mixture of veterans and recruits.
In the top-down view, this would allow us to create groups of mixed skill of archers, spears, sword, cavalry, etc. Then further assign these groups to different commanders.
As well as, reassignment of troops on the fly. A group of cavalry under the command of Baron Joe, may further be placed under command of Count Phillip and his swordsmen, as the battle progresses. While King Dave rampages with a section of cavalry. At any time, King Dave may break off from his sporting with the horses to come and personally lead the rabble of Swordsmen to victory.
That's my two cents.