I'm excited to see the leg kick portion of the engine updated. Taking damage to your legs screws up your mobility, power, and balance a lot. I am not sure of the overall role that balance plays in the fight engine, but causing damage to it and agility would make sense. You lose agility because your movements are hampered by leg damage and hopefully the loss in power would be reflected by the damage to your balance and inability to have a stable platform to fire heavy shots from. I hope to see TKO's possible due to leg kicks
I think some other areas of concern is that fighters that don't set up leg kicks leave themselves open to being hit with counter shots at the start of a fight. Another area that needs to be included in the fight engine is that if you defend leg kicks by checking them, you are decreasing your own mobility and standing in a fixed spot. This makes you a very good target for power punches. I.E. Renan Barao's recent knockout of Uriah Faber. Faber got knocked out when he tried to check a leg kick and couldn't slip or step out of the way of the power right hand. There are plenty of cases of fighters that lead with a leg kick with no setup that get blasted a counter right hand. Anderson Silva famously did it in one of his middle weight fights.
On the flip side, fighters with a very mobile style that fully utilizes ring movement and agility for striking defense often leave a leg behind as they move out of the way of their opponents strikes are going to get hit by leg kicks more often. This is how Shogun was able to constantly punish the trailing leg of Machida as Machida moved out of the way of the initial flurry.
An interesting fight to watch that shows a lot of the flaws and benefits of leg kick heavy strategies is Rick Rufus vs Changpuek Kiatsongrit.