The transmog restriction for Legion artifact weapons is removed. It probably also the time to upgrade old legendary weapons’ models, so people can have fun in transmog.
Legendary weapons we have:
Thunderfury - very outdated model
Sulfuras - very outdated model
Warglaives of Azzinoth - outdated
Thori’dal bow - outdated
Val’anyr mace - outdated
Shadowmourn - OK model
Dragonwrath - OK model
Fangs of the father - OK model
I hope at least Vanilla/BC/Wrath legendaries get updated. Their model details are seriously outdated today. ( e.g. upgrade Thunderfury at least to Legion outlaw rogue hidden artifact model level, and warglavies to DH artifact model level.)
I don’t think it will take much work. But it will be great for people who wants to use them for transmog.