a reason Arberter (however you spell it) should return:
The elites should be in a civil war. Half with the covenent, and half with the UNSC. Arbiter should be leading the rebel side (with UNSC).
along with the post above, with the the flood firefight thing, it should be kind of like black ops zombies, four different people like: cheif, arbiter, two other random people from halo. or just custom spartan IV's