Well, I seriously think it'll be franky. All my rumors I have on hand say otherwise, but then again, a lot of them are from huge fanboys, so take what they say with a grain of salt. I've certainly learned to. lol.
Oda's leading us too close to making Franky an official naka to NOT think he's going to be the 8th person. Which still begs the question about the Going Merry since you see it in the OP, yet it's supposidly dead.