There seems to be a lot of things that could be added. The types of thing that most studios already know Bungie especially.
Gear farming and new raids will keep people around. As long as you keep adding challenges to the game they will have no problem reaching their goal. Add in some mini games/objectives (dailies) will keep people there. I mean how many of you people spent hours chopping wood in skyrim? Should have a small house to display your armor sets or trophies for downing bosses in raids, or medals in PVP. There is alot they can do with this game. Bungie is just starting off with the ground floor and can build this game into something much bigger.