i think it would be cool to get some achievements which could give you some bonus flat dmg or resistence against NPCs ...
for example like something like u have killed x , y amount of geckos u get some archievement for it plus some PvE stat boost maybe , i mean maybe something like now u do +10 percent more dmagae to x , y critter or u are more resistent against their attacks or u have x , y chance if u encounter some NPC group and u have achievement that some of them will flee becoz u are some bad ugly mofo
, or they drop slightly better loot ... i even think this could be somehow connected with outdoorsmen skill ...
all this stuff could be done on different kind of npcs , like humans , robots , geckos , aliens , super mutants ... it could be divided even more into some specific human npcs group , for example yakuza killer or hospital mutant killer something like that