No, they clearly stated all quest items will unlock once Legion is launched, at Blizzcon.
http://blizzardwatch.com/2015/11/07/...ation-changes/
http://warcraft.blizzpro.com/2015/11...ransmog-slots/
They just never said, if those quests that give multiple choices, will unlock all items no matter who completes it, after Legion has launched. Which is what I was trying to get info on.
Ok, so it seems that quests that gave multiple choices are changed and only unlock items appropriate to your armor specialization. So, a mail wearer will only unlock mail, even if that quest included a plate choice prior to Legion, for example.
Long story short, do Loremaster before Legion is launched to have all armor pieces unlocked. Not sure about weapons but assuming it's the same, just as long as it is completed before Legion.