Sure, why not? It's off-season, the procs disable at 115ish, and they'll be going in the bank, storage, or sold to a vendor by the time we hit 120. BFA's less than a month out, let's go ham and see what sort of crazy shit people can churn out with a full complement of Legiondaries.
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Depends on the proc. Some that are pretty ass like the Antorus quest ring (where the proc really only works if you have an Antorus trinket which'll be replaced pretty quick) will be thrown by the wayside sooner than later, but free-DPS and shields/healing Legendaries are probably going to see a lot of action until the now-disabled proc no longer outweighs the raw stat gain you'll get from questing/dungeon gear.