Target Locator is my first pick. It might have to be restricted to Warzone Firefight. It could be overpowered for regular warzone or some specific gametypes.
I really want to see the Sticky detonator back as well. It was the perfect booby trap weapon.
Ok, well, some of these are extremely pointless. Flamethrower and sticky detonator would make unique additions to the sandbox though. I would love to do suicide runs with my friends again with the detonator.