We don't know for sure what's staying and going, and regardless Exotics should be relevant either way. Legendary shouldn't move on, but Exotics always should. I used a HammerBuster in Borderlands 2 in every new DLC. Just kept grinding for newer, stronger ones. But at the same time I looked for all the NEW Gold Tier gear to collect, and use. Just like people could do in TTK Bungie should just learn to balance their shit.