Well, the flashback pretty much points to VDD being the BBEG, with Princess Shirahoshi being foreshadowed as the catalyst for the island's prophetic destruction.
And the way i see it, per the basis of (possible) match-ups, luffy will be the one to face VDD, thus protecting the arc's central character (princess). Zoro vs. Hodi, and Sanji rescuing the captured mermaids by beating Caribou (sp?) to a bloody, filthy, dried-swamp pulp.