Bungie outright said cool your jets and don't dismantle anything until all the TTK details are released. I doubt anything is going to become useless... My guess is raid weapons will still be upgradeables. Which I hope is correct, because I just discovered the beauty that is praedyth's time piece and revenge in the crucible. I seem to be way more effective with them than I ever was with any exotic hand cannon and felwinters or party crasher.