I would have certain Quests for Guardians to do called Altered Quests". I have perfected a way to use a Vex Transfer Gate to go, not only alternate times of our worlds, but alternate universes altogether. These would be Quests that throw you in to another game's universe, that is in need of Guardian assistance. For example, taking a Quest called "A New Hope" would start a Star Wars questline. Taking a Quest called "Emergence Day" would start a Gears Of War questline. Throughout these questlines, you can get items called "Parallel Gear". What Parallel Gear is, is probably exactly what you think it is - armor and weapons from that game universe. As you play through, say, "A New Hope" (Which is part 1 of 3 of that questline), you can get certain gear from completing the quests. As an example, after *LITERAL ACTUAL SPOILER* [spoiler]Ben is killed on the Death Star[/spoiler] Hunters can receive Ben Kenobi's cloak and attire, Warlocks can recieve Darth Vader's armor, and Titans can get Stormtrooper armor. At the end of the questlines, you will recieve a Parallel Exotic, usually a weapon rather than armor. In the case of the Star Wars questline*, you would get a choice between Luke Skywalker's or Darth Sidious' Lightsabers. *There would be two Star Wars questlines, one for the sequels and one for the prequels. Obviously, this would never be a thing in game because of all the copyright issues, but I think it would be really cool to add this kinds of thing to the game. TL;DR There should Quests in this game that go to another game's world and you can receive loot from that other game.