I know this point has been hammered to death, but it is almost criminal that Bungie squandered so much of Destiny's story/lore.
Someone on Reddit fleshed out the first battles for Earth after The City was built, along with the Twilight Gap, based on Grimoire.
Like--holy shit, these would be amazing to see in-game. Either via godly CG or in-game engine.
Even better:
let us replay these historical battles as Strikes/Raids.
The Battle of the Six Fronts
-Unlock/discover the entrance of the House of the Devils
-Launch an assault on the House
-Retreat via vehicles back to the City after the Fallen swarm you
-Force six players to defend six separate strong points, using battlements/mounted weapons, as well as your own characters
Or something like that.
It would be pretty awesome if some of the named "heroes" of the struggles (Saint-14, Saladin, Zavala) would actually fight alongside you as NPC characters.