I thought about that as well, if it was something other than a weapon or a shield, all tanking classes could possibly wear it. Trinkets, rings and such can't have a cool model, obviously, which is probably the reason we haven't seen any legendary ones (nor do I want to see, as, well, they can't be seen

). Perhaps they also don't want legendaries to interfere with Tier sets.
Other pieces of equipment can, and have had, on-use effects / procs as well.
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