This one has so many suggestions!
As DLCs tend to be cultural packs, this one will start there.
Hyrkanians, Stormswept Steppes. This one had hoped Riders of Hyboria was going to be this culture. Built pieces may be limited, or could look like cloth or hide covered wood. Placeables should include yurts. Much like tents, but less open looking, something that is believable shelter. For gear, the Hyrkanians are sorta kinda Mongolians or other steppe horse nomads. This could include their own furs and lamellars, as well as heavier sets inspired by Yuan Dynasty China, which was Mongolian rules anyway.
Watch the movie Mongol and the Netflix Marco Polo for some of this one’s inspiration. But also Subotai from the Conan the Barbarian Movie.
Civilization, Ancient and Wicked.
A culture pack that would combine Stygian and Zamoran build pieces. There is already some Stygian and Zamoran gear, but this set could fill in the blanks for those. Also, a wish for a Khopesh that does not suck.
Lost in Time and Space.
A set that would focus on lost civilizations. Stormglass sorta works for Acheronian, but Lemurian or Atlantean build pieces. Gear already has been touched on a bit for Lemurians, so filling it out with an other, stranger styles may be an idea. An excuse to introduce bizarre looking arms and armour, possibly something vaguely reminiscent of the Meso-American empires
Also, this one would like to see a Black Kingdoms culture pack. Not just because this one likes Rungu club designs. Given how many different cultures could be covered under this umbrella, it’s an opportunity to include numerous looks and architecture from Benin, Akan, or the Bali Empire.
As for non-culture DLC, such as Siptah…
Honestly, one set in the ruins of one of the lost civilizations wouldn’t be the worst.
Alternatively, something not unlike Xuthal the city of lotus eaters or other isolated spot where an elder horror has posted up and thus may have an environment that doesn’t have to make sense, while still being populated by both friend and foe, and excessively difficult to leave.
These are DLC suggestions.
There are many features that this one would like developed into the game, but that this one does not think should be DLC.