I remember seeing a thread like this a while ago, and I would say large battles.
Gamebryo would explode with that many moving actors on the screen.
A thing they can do to get around that is have the player far away, maybe even commanding the battle from the top of a big, tall thing. As oposed to being
in the battle.
And since your far away, instead of having really good visual quality actors (which should slow it down), it can be so they don't have as good visual quality.
Maybe even so that your teammates only have backsides(since thats all you will be able to see), and your enemies only have frontsides (since thats all you will be able to see)
Or they could do what was done in Gears of War 2 (which let the designers have caboodles of characters on screen at a time). I have no idea how they did that, but if Bethesda could do that, then it would be happyness.
It may be confusing, but I think that if they could, I would love to see some large scale battles.
Maybe a huge raid on a city, or even between provinces would be cool. I would also like to have a part of the game when you command the battle, and whatnot.