I myself think that a follower system (such as the one in the Elder Scrolls V: Skyrim) could definitely be a part of Destiny. It is a very simple idea, it's basically hiring/paying another NPC, possibly from the last city, to fight with you on your adventures.
Ya but then you also have friends to play with and it becomes a cluster of gun fire from 5 different people, that (in my opinion) doesn't seem like the game.