What makes you so sure the method in the video doesn't use Powersaves? He clearly states he's not telling people how he did it and considering his other video showing a normal and shiny Diancie, it's very possible he's using a Powersaves. He didn't seem to pull the game out at any specific time, he just let Pokebank exit normally and then turned the 3DS off for about a minute. During that minute he's doing something else so the method being talked about with pulling the game out during the Pokebank part isn't what he did.
Not saying it can't be done some other way, maybe it can and it seems others have done it, but I think the video was done via Powersaves.