User blog comment:Xilinoc/Ch. 584 - THE HEADLESS STAR 3/@comment-1351982-20140611115731/@comment-1771627-20140611164600

There's all that thing about hollows being completely destroyed when they are killed by a quincy, but what about if they just vanish because Ywhach absorbs them through the quincy? All these years sleeping, he was slowly sucking up souls through all quincies left in the world so that he could recuperate from the seal. This would give him a fair amount of souls to forge even more than one key hahaha

Also, I theorize that the key have more purposes than just opening a portal to the royal realm, something that was not explained. Think about it, we just get the Oken can be used to open a portal to the king because that was Aizen's objective, though we never got a real explanation of what the Oken REALLY is.