Go full cav or go home
I'm a castle taker, mate. You need your arrows when taking a castle. (Because everyone in Warband is a handicap, and decides that entering a castle with 1 shield facing forward while arrows are shot at you from left & right is the best method of capture)
On that note, I also seriously hope that there's some sort of system for choosing how to perform a siege, such as whether you'll intend to use ladders, siege towers, or even battering rams.
And if you can have multiple ladders and towers, so that sieges aren't just a case of numbers.
It's pretty terrible when you have 400 men who just get killed one at a time as they walk single-file up a ladder.
And a better system for food within towns would be nice, since towns in Warband all have food to last weeks and weeks, so there's absolutely no chance of sieging a town and starving them into submission, since in the time it takes to happen there will almost certainly be an attack by other armies, come to end the siege.