he does? i dont remember that^ One problem with that theory bro; Aqua fights the creature PRIOR to the new Secret Ending, from the look of things...
Also, on the matter of Aqua using Ven's Keyblade; if memory serves me right, Terra was using Wayward Wind in the TGS2010 trailer for BBS:FM too, so it might be an unlockable keychain. Whether or not it has plot relevance remains to be seen...