+1 on the idea that: the more complicated the rules are, the more holes in it there will be. Given this I tend to prefer simpler designs. I've worked on a few Diku based MUDs, and at least on them completely separating PK from NO_PK characters would have been an ad-hoc mess. But I don't know how Arctic's code base has evolved with respect to target acquiring so I don't know how involved (and buggy) it would be.
I voted for PK. It was never my main focus, and nowadays when I play I never participate. That said, it being present changes how I play the game. But I may be biased since I usually can avoid PK if I don't want to participate.
That said, I've played on some games where pkill didn't cause you to drop a corpse. Players adapted and learned to "rkill" - real kill, which basically meant using mobs to finish players off. The staff approved of it, which added an interesting layer to player combat, requiring more nuance and skill than in Arctic's system.