Incorrect. From what we've seen in the stream... A weapon core is used to purchase the weapons that Variks will have for sale. Just like its counterpart the armor core will be used to purchase armor from Variks. He is like Xúr in the fact he will have different offerings each week. Weapon and Armor cores drop in PoE on differing levels. Guaranteed drops, Armor - Lvl 32, Weapon - Lvl 34, both - Lvl 35 Etheric Light is used to upgrade all Legendary gear (weapons and armor) to max light in year 1.