My guess is its going to work the same way it works before you hit lvl 20. All exotic and legendary items you have to be lvl 20 to use. White blue and green items all have lvl requirements to use. The new TTK weapons will probably have lvl requirements to use so everything you currently use will still be your best gear until your lvl progress to be able to use the new weapons as you acquire them. It's how the game should have worked all along. Now ppl can't rush to lvl 20 then buy gear to immediately be lvl 30+