I still think that Foxy is the next logical choice. But then again, so did I think before this story was revealed. But this time we´re really through with Skypieans so Longring Longland characters are next. Perhaps we might also see Tonjits adventures. But if so I hope just for a couple of pages (like with the recent story, when we saw Gun Fall, Wiper and Konis before Enel appeared). I just think that Foxy has more potential then Tonjit.
After that the Water 7 characters would be the next ones. While I do think that T-Bone is side story material I would really be greatly suprised if we don´t see how Iceburg turns Water 7 into a floating island. That has to appear somewhere. Just think back of Drum, they´ve spoke of the election but when the Strawhats left that part wasn´t decided. It was Wapols mini story in which King Dalton of the Sakura Kingdom was introduced. The same would actually make sense for floating Water 7.