If you were to compile all the Stormblood dungeons we've gotten in all of the patches you may notice something.

61: Siren Song (Technically from Limsa going to Doma but marked as ???)

63: Shisui of the Violet Tides (Doma)

65: Bardam's Mettle(Doma)

67: Doma Castle (Doma)

69: Castrum Abania (Gyr Abania)

70: Ala Mhigo (Gyr Abania)
Temple of the Fist (Gyr Abania)
Kugane Castle (Doma)
The Drowned City of Skalla (Gyr Abania)
Hell's Lid (Doma)
Fractal Contiuum Hard Mode (Albathia's Spine/Azy Llha)
Swallow's Compass (Doma)
The Burn (Doma, yes it is still considered Doma)
Saint Mocianne's Arboretum Hard Mode (The Dravanian Hinterlands)
The Ghimlyt Dark (Gyr Abania)

We can add up the totals of these dungeons as well based on region:
???: 1
Albathia's Spine/Azys Llha: 1
Dravanian Hinterlands: 1
Gyr Abania:5
Doma: 7

Gyr Abanian areas are incredibly underutilized as opposed to the Doman ones. As the story for 4.0 drifts around 60% Doma and 40% Gyr Abania. Now that we have given them liberty (and warded off the Empire as of 4.56 for the time) it would be fantastic to have us visit an area not properly utilized during the Empire's reign over the nation or to revisit a previous area and see a completely new take on it.

If you would like some recommendations here are some of my personal thoughts!
Dimworld: Possibly going into the Saint Mocciane's idea, but I'd love to see a marshland explored or even the caves where the White Mage 70 Job quest takes place.
Nyunkrepf's Hope: The giant ship that is hanging out in the Peaks. It was used by people living in the Hinterlands to travel during the raging storms of the Sixth Umbral era and ended up being located in the Peaks. Those going on the ships would later form Sharlayan which we've all become accustomed to but the ship remains still in the canyons. I'd love to have a dungeon to explore it as it would be a great chance to show more Sharlayan lore but could also have The Peaks related enemies to fight inside it (assuming they're using it as a nesting ground).
The Ziggurat: The huge upside down pyramid we visit originally during the our first visit to the Peaks. I feel like getting a chance to explore the inside of it if possible. I imagine something of a tomb like Qarn, but maybe exploring the top of the pyramid and fighting a cool griffin or something native to the area. It's filled with lore between Mhachi and Ampadori so it would serve as a fun callback to the two of them.