I've been requesting nth is for a while, and my reasoning would be that it could have a final slot in the upgrade tree (much like the Husk of the pit) in which any weapon would require a total kill volume while the weapon was being used, for example1,000 enemies killed while being used. At which point the gun would reset just like an upgraded exotic. And each expansion, with each upgrade, the kill volume could increase by 1000. Just a suggestion.