There's a little snippet of information from Jack Lusted about battles in the official forums https://forums.totalwar.com/discussi...-and-mechanics
A few key points:
Shield Walls and Shield Castles are in.
Formations are tighter than what we've seen in the released images and videos, and Shield Wall will apparently be default for appropriate infantry.
Cavalry react to infantry in stationary formation differently to anything we've seen in TW before when they charge head on (I love this bit and can't wait to see the animations).
They're aiming for 12-15 minute battles between full stacks.
Holy hell the news from this Saga just keeps getting better.