The easiest solution IMO is, just have the newest upgrade mats from the current raid be required to upgrade previous raid's gear. Say, 10 Radiant Energies and 5K Glimmer to upgrade to the highest damage available, but only after it's upgraded fully at the 300 level, and then re-upgrading it would still need to be done back to 331 (Bungie loves dat grind). Another option is to treat them like exotic weapons are now. Hell, create a legendary shard for the trade in requirements. All sold through Xur. A few caveats: 1. DLC is required for any upgrades. 2. More vault space would need to happen (it already should be, obviously). 3. Only raid drops have the ability to be upgraded. A side note: If they would just add a modifier to VoG to increase the difficulty, similar to missions, then that would keep content relevant for the foreseeable future, while allowing the drops to have equal damage across the raids. Just make buying the most recent DLC a requirement for these harder modes.