One of the combat aspects I hope the most for to be innovated are combat width and reinforcement. While it's nice to have the battle of Verdun simulated in vic2 it doesn't really reflect reality. Having a battle ingame go on for weeks or months in just a single province is nonsensical. An innovation could be that battles escalate, so it starts with 5 combat width and recon troops like planes and cav, and then increases combat width over time to allow more and more troops to join in, further expanded if troops from adjecent provinces support. You could end up with combat widths of 30 or 50 to allow massive battles like the one Leipzig against nopoleon with hundreds of thousands of troops to be resolved within days instead of weeks terrain should only limit the speed at which a battle escalates and forts should be the factor that ultimately limits maximum combat width.