Guild wars 2 is probably the best example I've seen of an organic need for players to work together while exploring. A giant troll comes our of a cave and it takes anywhere from 10 to 45 players to kill it. Or a mini boss in the northern mountains that's trying to summon a dragon god and requires AT LEAST 20 players. I'm not asking for bungie to give us that many players, the old systems couldn't handle it, but the bosses that require guardians to band together and win would feel so accomplishing. More so than a raid the more guardians it takes.