As Voidrig is range/all-round mecha, he does not have any melee "weapon" at all but compatible with modern Archguns. And DE say Bonewidow will be a new Necramech focus on melee and shield, I expected Bonewidow to use only her own grenade launcher and be compatible with modern Archmelee apart from her own.
But what I see from this seems more like otherwise, she can equip any Archgun like Voidrig, but for melee, she can use only her own (as an excalted) making her still be a gunbot like Voidrig.
Not to mention that Archmelees are relatively crap and rarel