I'm pretty sure all the quests we've DONE before will get added to our Wardrobe anyway, so we don't need to bring them back, only people who didn't do them prior won't have them. I'm assuming this means for all the old quests that didn't change depending on your class/spec etc, you'll unlock them all.
http://www.tentonhammer.com/guides/l...cation-changesNo longer will your storage be totally taken up by old item sets, every item that is bound to your character will be added into the Wardrobe. This includes items from old quest rewards that you may not have picked, which will automatically be added into your Wardrobe at the launch of Legion.
https://www.youtube.com/watch?v=tcMzjPpQB-c (No idea the time, but that's TTH's source so it'll be somewhere in there)