I'd like to make a suggestion for a cave race: The Pale Ones (Agartha)
If you've played a Dominions or Conquest of Elysium game before, you'll know right away what they are.
However, here a short description.
They are cave-dwelling, amphibious (live as well on land, the Pale Ones, as in the sea, the Wet Ones) one-eyed humanoids with exceptional vision in the dark that live for a very, very long time. The older they get, the larger they become. Old Ones are essentially giants, a few times the height of a human. The younger ones are probably human-sized, perhaps a little taller. They get their name because of their pale skin, possibly caused by a lack of sun in the caverns where they live.
They are not the most formidable fighters; a bit clumsy perhaps compared to other races, but they are tremendously strong, to the point that they throw rocks at enemy fortifications, where puny humans would have to build siege equipment. So, really strong. They mostly use spears to impale their enemies (note: spear sounds so mundane when you consider the size they have; they are more like oversized pikes). Only the most honored tend to wear "full body" (basically just a breastplate) armor, most Pale Ones forgo the use of armor; there are layers and layers of tissue to cut, and cut deep, before any vital organ could be hit anyway. Most small weapons will have a tough time as is, without them being armored.
The Pale Ones are also versed in a few schools of magic which might not necessarily need to be represented in dwarf fortress. One however very well could: Necromancy. It's not unheard that Pale Ones call upon their elders, the deceased ones that is, and bring them back to life to fight for them. Similarly to animating their own dead, they also animate and imbue the elements with life, commandeering Rock Elementals and Fire Elementals.
The Pale Ones keep troglodytes as we keep pets; except troglodytes are enormous, although relatively stupid, beings. They don't use any weapons, but rely on pure strength to stomp their enemies to death. They are larger than most young pale ones and could possibly challenge a cyclops in smaller groups.
Oh, before I forget, the Ancient Ones (so the really old guys) have neat magic weaponry, which could possibly be modeled by making them out of a new metal. Although those weapons would be unusable by dwarves due to the size difference, dwarves could get their hands on that metal by melting it. Could quite possibly be somewhere between steel and volcanic. It's magic after all.
Here you can read about their lore:
http://dom4.wikia.com/wiki/Agartha_(Early_Ages)
And here you can have a look at some of their units, along with sprites to give you an idea:
https://larzm42.github.io/dom4inspector/ (Go to the units tab and select EA Agartha - Pale Ones).
So in summary:
Giant pale humanoids, one eye, very strong but not agile, very tough. Can swim, is amphibian. Few are armored, but their thick layer of tissue helps mitigate a good amount of damage even if unarmored. Preferred weapons would be spears. Elite Pale Ones carry magical weapons and armor, which could be melted down to acquire a better-than-steel metal for reforging in dwarf-sized armor/weaponry.
Could also field some undead variants (Reanimated Old Ones, necromancy -- Umbrals). Could also field rock elementals. Does also field Troglodytes, huge but stupid creatures that don't use weapons but trample/punch things to death.
If you have any questions regarding this, please let me know. I'd love to clarify!
PS: I voted in favor of more regional effects, whether and such, as I supposed everyone else would vote for CIVs anyway (yeah, yeah, I thought too meta here) only to see few people did. Note that I only voted for something else than CIVs because I believe them to be an integral part that will be included either way, or have support either way. So in a sense, I voted for my second pick. I'm sometimes stupid like that