In terms of revamping the battle engine, I’d like to see the battles slowed down a bit, less micro-management and less click-powers, more focus on formations and on units maintaining cohesion.
Here is an old thread with some battles reports from the original Rome: Total War. I’d like to see an engine generate more battles like that, especially the Spartan Ambush I described.
I love TW: Warhammer 1&2 but even with a fantasy background, I’d like to see more stable battles. And for historical stuff, definitely.