I like vorpal, but given how situational it is, on something like a primary, its only useful for endgame content or champions. So I think moving forward, it should roll as a 3rd column perk for all primaries, and for unique heavy weapons or special weapons like raid, dungeon, and nightfall special/heavies weapons. Personally, I'd love to see something like frenzy + vorpal combos or vorpal + deconstruct.