Mentioned this in an earlier post but figured I'd put it into the idea section for comments. The idea works as such: when the rare limit for an item has been hit the NPC will still have the item visible on their person and it can still be seen on them using locate object. The item will be marked in a way so that players will know that it isn't technically there so they don't waste time going to farm it.
Not sure what the best idea for the marker would be but something like this:
When an item is equipped and will drop on death - A large two handed sword
When an item is equipped but won't drop - A large two handed sword
Benefits of this feature are mostly for new players. If I'm a Warrior I can look at what the other level 50 Warriors are using and write down the equipment and explore later to find out which mobs have it. If Karashin has an epic piece of armor/weapon and others do so the rare count is hit then no matter how much I explore I won't ever see it on the NPC so I'll never learn where to find it. When Karashin dies if he looses the piece he'll most likely be rushing back to go get it since he'll know it's available so it's gone again, if the one who beat him takes it it's still gone.