Well, it doesn't really need to be gold and jewels either. One Piece can be anything Gol D. Roger considered his treasure, just like Luffy consider an old strawhat his treasure.
Right I agree! But hey adding a giant golden block can't help but add to whatever he defines as Treasure XD!
EDIT: Just had a thought....while Skylar Knight and I had discussed a Impel Down return on the last page I thought that it may even tie in with the "Great Battle"....basically you have Luffy up on the chopping block, and probably the rest of the Straw Hats manage to get away (I.E. Zoro and Sanji successfully rescued from Impel Down, but Luffy wasn't saved).
Then you have the return of the Whitebeard Pirates under Marco, and begin a second attempt to fight Marineford along side most of the Strawhats
Then through maybee Robin's Revolutionary contacts and the rest of the Straw Hats' friendships they manage to grab old time allies and enemies like Franky's House, Galley La, CP9, Fishman Island (Jimbei and maybee even Shirahowshi controlling Sea Kings), Vivi with an army from Alabasta, an army from Skypia...maybee even Enel, Maybee personal interest Crocodile, and the Rebolutionaries like Dragon and Ivankov.
And part of the plan would be loading up these allies (aside from the Whitebeard pirates in the already made Pluton that is in Alabasta (Robin knew where it was)!
That would be pretty epic