If Arrowhead were to go back and add a fifth weapon and a third armor set to the Legendary Warbonds, what would they add?

Obviously for Halo it would be the Spnkr as a strategem, but I don't know enough about Killzone and Warhammer to reliably guess. Maybe they'd add the StA-18, but that would be a bit of a letdown even if it would round out the Halo warbond having an AR, an SMG, and a power weapon.