I keep being reminded of those card games like Magic the Gathering or that card game from Final Fantasy VIII (http://www.youtube.com/watch?v=264wi-_Yxmw) when looking at the Grimoire cards you collect whilst playing Destiny. I can't help but help but wonder if they could be incorporated in-game, either through a social player to player interaction or a NPC to play some form of card battle game? I wouldn't expect anything overly complex, but a simple and easy to grasp game could be a fun addition to Destiny and make for a nice distraction between missions. Perhaps players could even compete/gamble for a modest reward?