More patrol areas. Old Chicago, Europa, and a Jovian area, somewhere where we would either fight or work with the nine. Either Savathûn, the cabal empire en masse, or a new fleet of fallen houses could attack. Or potentially a new vex axis mind, although I think that would be rather boring. Extra awesome things that bungie could do. Phobos as a fleshed out planetoid. Make public events full on battles, increase the max amount of people in a patrol area, and add some serious firepower into the enemies. I'm talking a giant fallen fleet coming out of orbit and trying to claim a patrol area. Say you're in the sky watch. All of a sudden, the sky goes dark. Ten, maybe twenty skiffs and a fallen ketch soar above the map. The ketch lands and out comes two or three heavy pikes. A few like bands show up. The skiffs drop two or three devil walkers and then start firing at players. Hordes of fallen swarm the cosmodrome. Ultra's, like a fallen commander, or maybe a powerful minor priest arrives. There could be high servitors, and if the players survive and kill the enemies, the fallen kell of the appropriate house shows up. This could also be the prime servitor or the archon. The kell isn't able to be killed, he teleports away at the last second like an enemy at the end of a public event. Also, add stuff like on the dreadnaught into the other areas. I would explore mars for hours if there was a real incentive too.