What about customizable player spaces, like your own mini version of the tower or the reef, but in the form of a large ship. These places could be filled with trophies for getting achievements, like Crota's sword on the wall for soloing Crota, or maybe a shield with the Lynx on it for going unbroken. These places could be accessed by yourself and friends only through invite, or maybe make them public to show off to others, and should have different themes like Hive, Fallen, Vex, Iron Banner, Trials of Osiris, etc. And these personal ships should have a hanger where you can display your sparrows and ships. As well as this, a vault that you can share with your friends and trade with them would be cool too. Also a place to display your favorite armor and weapons would be a good way to show off your year one items to prove that you are a veteran without worrying about dropping light level.