The next expansion for Destiny, House of Wolves, will allow players to keep older gear viable by upgrading it with a new resource called Etheric Light.
Bungie explained the new system in a livestream presentation today (as reported by Polygon). Using one Etheric Light, a resource dropped in the new Prison of Elders endgame content and PvP Trials of Osiris, any piece of Legendary equipment can be upgraded to its highest level. For weapons, this means max damage can reach the new 365 cap, and upgraded armour will be sufficient to reach the new Light Level cap, 34. Etheric Light will also drop during Nightfall runs and the Iron Banner event on occasion, making it possible for those who don't have House of Wolves to reach the new cap.
Exotic gear can also be upgraded using an Exotic Shard (among other resources), and players will no longer need to use the services of the weekend vendor Xur to do so. The Speaker NPC at the Tower will also offer Shards in exchange for Motes of Light, and let players swap Ascendant Shards and Radiant Shards for their respective energies, and vice versa.
Finally, the new Legendary weapons added with House of Wolves will be able to be reforged at the Tower's Gunsmith, randomly changing the perks attached.
These new systems follow widespread criticism of gear upgrades with the first expansion, The Dark Below. Due to the increased level cap and new gear introduced at the time, equipment earned from the Vault of Glass raid - which had been the game's most difficult content - was rendered obsolete. As a result, many players felt like the time they'd spent on the Vault of Glass had been wasted.