Killspeed can already be modified. However some mods prefer to fix it by giving lots of morale to the troops.

Movementrate could also have been moddeable if we had a proper tool for importing and exporting animations. CA hasn't released it during the last 2 years so I have little hope that this will change. Especially with CA saying that they will give the same modding support with tools as they had done with R:TW (that is 0, CA!)
My personal rub is "line cohesion" Saladin's battle line was disintigrating into individual unit attacks before they even reached Richard's infantry line.
Line cohesion should have been the first thing they coded for the AI. That doesn't sound promising at all.