With the Pokemon Bank opening up in a few days/hours, a LOT of people are going to find their legendaries are being traded for crappy Feebas, Meowths, Cottonees, and other legendaries like Arceus.
The real question is, will the GTS block the hacked/unvalidated Pokemon from even being traded? So far all of the Pokemon found over the GTS are ones that are valid catches (either in-game or via the Friend Safari), so we have no idea if Arceus will even be tradable.