Another, related, idea popped into my noggin....what if over-powered enemies can try to surrender?
I know most times even if they ~try~ it'll take the PC too long to realize it and they'll get killed anyway, but if you're consciously looking for an opportunity to spare a foe, for some good karma, that would be a nice feature.
The catch, though, is that the foe that "surrenders" CANNOT then immediately grab a gun from the ground and start shooting you again. I forget which game it was, but there was one game (Skyrim?) where foes would plead for mercy and even if you stopped attacking them, they would come back to attack you in short order. While I can see where some foes ~would~ try that tactic, when -every- foe does it, you just know that there's no point in sparing a foe.
But what if there -was- a point.
What if you got experience and good karma from surrendering foes? They might or might not drop / offer their loot to you, but I can understand that "losing" the loot they may have would be the price for the good karma.... I wouldn't be heartbroken to lose a set of broken raider armor and a lead pipe and a bag of chips.
Of course, you get good karma for ~killing~ raiders, too, and all their loot so the good karma / exp would need to be worth the extra step of sparing a foe. If the foe is legitimately fleeing, and you let them, they should run off screen and despawn (as 'rescued' prisoners sometimes do). Of course, if they surrender --- perhaps being required to relinquish all their weapons and loot ---- and then the PC attacks and kills the helpless, surrendered foe, then the PC could acquire ~evil~ karma, even though they are killing a raider.
Killing a raider = base good karma
Sparing a raider = extra good karma
Killing a raider who surrendered = evil karma
Killing a raider who surrendered but then started to attack again = base good karma
In particular, this would be great for a non-lethal play-through where, for example, you shoot weapons out of foes' hands and/or melee them and try to knock them out or make them surrender instead of blowing them to bits.
Of course, sparing a raider may NOT be 'good' karma... since it's unlikely your mercy will change them into good people; they may still be raiders and go on to do evil things, so maybe getting good karma for sparing them isn't the answer.