@Triceron:
I was watching the latest episode of the anime, about Madame Shirley. I think that chapter foreshadows what will happen when the Strawhats meet Big Mom.
In that episode, we see the Candy Factory and Big Mom's flag for the first time. Luffy mentions how he'd like to meet her one day. At the end of the episode, we have Madame Shirley making the prediction that Luffy will be the one who destroys Fishman Island.
In this issue, and we have Luffy and Big Mom talking directly for the first time. They're obviously not on good terms, and Luffy even says he will beat her up and make Fishman Island his own.
My theory is that Luffy might actually destroy Fishman Island as a direct attack on Big Mom. Now I know that wouldn't make sense since he wants to protect Fishman Island, not destroy it, but here me out.
Fishman Island is Big Mom's territory. The Strawhats will eventually leave to the New World, having no means to protect the island. After they leave, Big Mom changes the the entire island into a giant slave-factory with all the Fishmen and Mermaids forced to make candy. She does this as a punishment for missing the candy delivery. Time passes, and the Strawhats eventually learn about what has happened and return to Fishman Island. Now Luffy has a good reason to destroy the island, freeing the fishmen from slavery and fulfilling Shirley's prophecy at the same time.
I think Luffy is gonna blow up the factory.