To be honest I'd much rather see D&D handle mass combat like Flashing Blades does. IE: No miniatures, no maps, just tables.
Players decided if they are going to act cowardly, timid, normal, brave, heroic.
This effects the chance of them getting a single combat, wealth gained on looting the battlefield, possibility of capturing an enemy standard, etc.
If they are commanding a unit then they get a chance of a brilliant tactical that could help change the out come of the battle.
The Army and Division commanders on each side effect the final outcome of the battle and the players actions depending on the results of their combats also effect the result of the battle.
If I want to play a wargame I'll play a wargame I want to be able to resolve mass-battle within normal play.