It's interesting because the uncovered area of Yok Tural is roughly equal to Aldenard, and we had more than two expansions worth of zones in Eorzea, but it comes down to their design philosophy choices of how much of the map do they convert into a single overworld zone. I doubt that Yak T'el will encompass all of the "rainforest" region that has two very large river systems and that suspiciously uniform sideways omega plateau with cenotes. If I were to guess at additional zone maps staying within southern continent and knowing that the world map is too zoomed out for many features, I'd guess a map north or south of Yak T'el that has some dense rainforest sections for visual continuity but has a river as the central feature instead of cenotes and a zone inspired by the pampas grasslands of southern Brazil, eastern Argentina, and neighboring countries. I don't think we'll get a region inspired by the Atacama Desert because of the abundance of desert zones already, though with each new whale fossil discovery it just reminds me of how much I'd love if this was a proper FFX inspired expansion with another Sin-inspired trial boss that isn't Bismark and that we'd fight 'totally not Sin or Bismark' in a coastal desert region south of 'totally not Peru'. The suspicious northern crack screams 6th zone to me- but I'd also love if a cenote leads into the 6th zone and it's inspired by the Afterlife.