I think that being able to customise things like knockout-turnframes and knockout-threshhold would be important. I also think that maybe this could be an option for all joints in some mods where the joint itself is relaxed for that period of time. I feel like being able to immobilise joints temporarily in this way in mods with tend to last longer would be preferable to the fracture system which tends to end up being more annoying than realistic. Maybe I am overthinking this (as I often do with such suggestions) but I feel like it would be a stylish way to reward ambitious attacks in mods where such moves are risky without it devolving into whoever gets the first snap kick dm inevitably wins (the fact that the joint/whole body is relaxed only temporarily allows players to recover if they are in a good enough position to start with). I am not exactly sure how the damage/force system works with fractures and dms so I can't really say how it would work, but I think it would be important that only actual kicks/punches could score knockouts rather than just applying enough force to the head/joint with a grab.
Sorry if I got overexcited, I honestly think this sort of mechanic would help advance the game's style and realism. Think about how ridiculously awesome the Wushu Punch preinstalled replay looks and imagine if that could happen at least every couple dozen fights or so. To me, this sort of subtlety is what toribash is in need of, I meant, fractured joints look hilarious and dismembered limbs tend to end up looking absurd. Giving mod makers the option to trade fractures for knockouts would be very exciting to me.