After spending way too much time looking at this, I only wish there were more facts and fewer speculations.
Anet can mess this up pretty bad, be it for the people who crafted multiple sets before this, or the people interested in fashion, or for the people who just want to participate in the end game freedom that legendary gear provides. They're kind of in a rough situation with this; so I'm just gonna throw in my thoughts to this too and hope that it's actually considered.
in regards to players who have already made duplicates of legendaries; offering a way for them to use their duplicates would be nice, either by just unbinding them so that they can sell them to other players, or by making them useful in some other way, like as an exchange for a special new rare item. Giving full refunds for the crafting of each legendary would have a lot of issues with implementation and still leave players with a lot of legendary crafting materials that they wont be able to do anything with, and I think it would be a bad idea because of that.
For players who care about style; either allowing them to make a "fake" duplicate legendary for the purposes of wardrobe (maybe at the cost of an ascended item of the same slot, or exotic) would be an easy step that wouldnt require a new system, but I also think that it's about time we have wardrobe loadouts be different from equipment anyway. Style is an important part of the game to many people, being able to save "wardrobe loadout"s and sharing them is a long overdue thing, and with people running around in full legendary gear being more of a reality, having different styles that can just go on top of that (for free) is important. in an actually useful part of this, I like having different visuals for each of my builds so that I can tell at a glance which stat set I'm running, if we can't have different styles for different loadouts on legendary armour then there's almost a detriment to having legendary gear vs having multiple sets of ascended, and that shouldn't be a thing with how tough it is to get the gear in the first place.
Lastly for everyone else; if the restrictions for this new system are too strict (ex: the armoury only can steal the legendary from another character without going to character select) then the whole thing will honestly just be a waste of everyone's time and hopes. We all like this game, that's why we're still playing it, throw us some QoL bones that don't cost us gems once in a while, please.
Thanks