The biggest problem I have picturing Hodi as main villain is that his character just screams "I AM NOBODY". He is like Foxy, beating him just won't be merit enough for the future Pirate King. In East Blue Luffy beat all the big bounties, in GL he beat two Shichibukai, "god" and Rob Lucci while befriending two more Shichibukais, all of them major feats (even though not all is public knowledge in the OP world). Luffy is gonna need a big opponent, a new impressive feat to his long list. Hodi doesn't seem to be that famous outside FI and NFP seems to be fairly newly formed. Similar to Enel perhaps, but Enel was revered as god in Skypiea, while Hodi seems to be just the boss of the fishman district thugs.
Sea God Neptune could be the next big victory for Luffy, but if he does turn out to be a good guy, I'm betting the man in shadows is going to be someone big in OP world, and is using NFP as merely pawns. But wouldn't it be appropriate for the next Pirate King to have defeated the god of heaven, the god of sea and the god of land (Sengoku, would be a waste not see him fighting, he also seems pretty equal with legendary Garp and I seriously doubt Luffy and Garp are ever gonna fight seriously).