It's gonna end up being a laser/plasma cannon that needs to charge like a fusion rifle. It is probably specific to the strike and maybe show up in Prison of Elders during a "boss" or mini "boss" fight. You probably rip it off a Vandarchon and get to use it against tanks, massive servitors (and massive shanks =]), new Fallen enemy type etc. Seeing as there are 2 in artwork and only 1 on the Vandarchon, I'd assume there's more than one of the Vandarchon. Silly theory, but isn't one of the missions Vex related, where Skolas goes to the Citadel? What if it's a modified Minotaur laser blaster paired with Fallen tech in the place of the missing arm?