If any of the Straw Hats is going to show up, it's Robin, since she made made a connection to Dragon via the Revolutionary Army. Also, chambers' suggestion that the Bridge of Exhaustion is a project to connect two of the three major government facilities is pretty good -- it makes more sense for it to be a bridge between Enies Lobby and Impel Down, though. Either way, she is relatively close to Mariejoa. Speculative, at best.

I wonder what role her meeting the Revolutionaries will play in the plot. Are they going to ask for Pluton to use against the WG? That would probably be the WG's worst nightmare. It would be pretty amazing if Robin figured out Luffy would go straight to Ace, and showed up at Mariejoa on Pluton with Dragon.