Not sure if it's worth mentioning, but Abalathia's Spine is the main mountain range of Aldenard and is populated by the Hellguard Roegadyn as well as poor villages of Midlander Hyur. Don't think there's much of a reason for us to go there though since Edda and Avere left there to become adventurers elsewhere and the Hyur settlements never get mentioned again. The Sea of Clouds is in part of it but we just visited it because floating islands are interesting and the devs wanted to show off zones with 3 dimensions and flying.
We're still missing other sections of Aldenard like West Shroud, both sections of Coerthas Lowlands that we got a glimpse of while fighting Gilgamesh, and Coerthas Northern Highlands (where Estinien is from if memory serves). Paglth'an and Xelphatol feel like they got cheap cop outs for squeezing in gigantic swathes of land on the game's home continent with dungeons that quickly become obsolete.
Speaking of dungeons, 2 future possibilities for dungeons inside Eorzea are the missing city-states from the 5th Astral Era. I believe we were told there were 6 but we only know of Mhach, Amdapor, Nym, and Skalla. The Nanawa Mines were a dungeon in 1.0, but now are just zone lines and the whole thing is skipped when you zone between Central Thanalan and Northern Thanalan
In Ilsabard there's some more places that got mentioned like Zetina's Grace and Martrvje in Bozja. Martrvje itself would probably be the de facto capital of Bozja due to Bozja Citadel itself being melted. It is said to be a port city and home to 200,000 people and other than Landis is the unseen city I most want to see.
Mons Falconis is a town in Landis large enough for its own gazette. Mannatheihwo is a city in Landis that used to have an order of Mage Knights. Arnsbeirgs is another settlement in Landis where the Gabranths and Lyon are from and could be the capital.
For Othard, Revenia is a settlement in Dalmasca large enough to have street urchins. Neimrahava and Sal Ghidos are other settlements in Dalmasca that got a passing mention.
And there is a lot of unexplored Doma. The mountains have Raen petty-kingdoms that get alluded to in the NIN questline.