Thanks! Are we talking a simple enough job if knowing what you're doing or would it take a lot of work?
Depends on how complicated you want to make it. A random critical hit chance, based on existing attributes like luck, weapon skill, fatigue, etc. that multiplies regular weapon damage - pretty easy. If you want it more polished - play a special hit shader or sound effect on the target - that's slightly harder. If you want something like a dedicated "CriticalHitChance" stat, then that's harder yet. Overall, I'd estimate about a weeks work from start to release for an experienced plugin maker.