Raid(s?)
When all is said and done, what keeps players (PvE ones particularly) sticking around is the endgame content. For the most part, that content revolves around Raids. Huge, hour plus long missions that have a team of six Guardians complete multiple tasks, kill hundreds of aliens, and defeat a series of challenging bosses. It’s the reason why so many players spend hour after hour grinding for better gear in all of Destiny’s other content.
The Taken King came with King’s Fall, but there’s but so many times that players can repeately play the same content. The two older raids, Vault of Glass and Crota’s End, didn’t receive any upgrades with Year Two, so playing those is relatively pointless unless you need the achievement because you just got the game. Their weapons and gear stay stuck at Year One values, so grinding them out if you aren’t really a PvP player will do nothing but fill a slot in your Vault.
Sure, there’s Challenge Mode for the King’s Fall raid now, and for a while that will keep players coming back, but once all of the emblems, ships, shaders, and weapons are collected those players will be able to say, with confidence, that they’ve beaten The Taken King. What then?
With the focus on events that Destiny is adopting maybe they can shake up the system of Raids, as well. A temporary Raid that gives players the opportunity to earn some truly unique gear, or perhaps new events that expand upon the older Raids that have been pretty much left in the dust with the advent of Year Two. Perhaps Bungie can provide a Cabal-centered Raid as a sort of last hurrah, finally giving a challenge that pits players against each of the enemy races.