I've had some ideas for new civs. There are some things that modding would not be able to deal with.
Western:
Trow/Deep Elf:An underground race of elves that grow fungus and tame cave creatures. Could be more martial than surface elves in response to underground threats, using bone or chitin arms in addition to wood, or reactions that harden wood or they cultivate special iron-wood fungus that is much harder than other wood.
Most people would probably recognize the spelling Drow instead of Trow, but I'd rather shy away from Gygax's version since people want them to be so specific sometimes. Trow is actually cognate to Troll and represents a diminutive version, although the Trolls of the Norse world bear little similarity to those of Tolkien and Gygax. Trolls were associated with magic; the term trollman refers to a magician or wizard.
Powrie/Redcap:A predatory race of dwarves that lives on the surface. According to legend, they dyed their caps red with blood, and had to kill regularly for if the caps ran out of blood they died. I would just say that Powries are bloodsuckers and starve without sustenance. It was impossible to outrun a Powrie, either because they are too fast or because they are tireless. Powries lived in the ruins of old castles. In dwarf fortress they might take up residence in ruined sites, but this would complicate world generation. Perhaps Powries could build sites that appear to be ruins, being in a state of disrepair or unfinishedness, or being eerily empty on account of the blood suckers lack of needs.
Barbarian/Wildmen:A relative of the common human with greater physical ability and animalistic instinct. They could live a nomadic lifestyle traveling in huge groups and making temporary camps, or they could live in crude dwellings, hardly sheltered from the elements that they do not fear. Barbarians might specifically colonize savage ecosystems, or human sites within savage ecosystems might generate or transform into barbarian groups. Barbarians would ride on exotic mounts or carry their goods on exotic animals like elephants and rhinos. Barbarians would wear garments made of hides, bones and shells instead of cloth, and might forego the hassle of metalworking and rely on wood, rock, bone or shell arms and armor instead.
Puck/Brownie/Hob:Small mischievous spirits of western lore. I would imagine something akin to Terry Pratchett's Nac Mac Feegles, very small creatures with enormous strength. They would probably prefer to fight barehanded than with weapons, as they wouldn't be able to wield anything particularly dangerous, although, I enjoy the Atelier Iris version of Brownies which are knee-high little munchkins that wield stone hammers as large as they are and I would love some sort of tag that would make that possible. AI's Brownie:
Not sure what kind of site a Puck/Brownie/Hob would occupy. According to some myths they live inside mushrooms, maybe they could grow a kind of highwood sized mushroom and hollow out the cap to live in, with multiple caps together to form large buildings like the civic mound or drinking hall. They could also roam the world as vagabonds or live exclusively in existing civs, like animal people.
X-Taurs:Centaur like creatures made from various animals. They would probably be like animal people. In contemporary artwork, they are often depicted as fully animal, but with a hexapod body layout.
Some examples. Fair warning, they are weird:
Wolftaur:
Lizardtaur:
Liontaur:
Horstaur:
Humantaur:
I couldn't find good birdtaur in contemporary art (maybe I should draw my own...), but there's a southeast asian creature known as the kinnara which is like a bird centaur:
Indian:
( I realize that many would complain that Indian mythoraces are out of character for DF, but they might provide the foundations of an idea that could be DFized later )
Rakshasa:The antagonists of the Ramayana are a race of "demons" with the ability to fly, venomous claws and taste for human flesh (presumably also dwarves and their boozey livers). Some sort of EATS_PEOPLE tag could work like the thief and snather civs for Rakshasas and Powries. Rakshasa seem to be prone to mutations, their king, Ravana, has 10 heads and 10 arms, his brother Kumbhakarna was a giant, and in artwork, the rakshasa are often portrayed as various animals rather than any specific shape. They inhabit a fortress atop a mountain on an island, very difficult to reach if one is not able to fly like a Rakshasa. This could be an interesting type of site to add when ships are implemented, as it would require sea travel to reach. (Although in the real story, the Vanara use a dwarfier approach and reach Lanka by building a bridge hundreds of miles long and exploiting an error in physics left by the gods)
Some pictures:
Vanara:One of the main protagonists of the Ramayana are the race of monkey-men, the Vanara. The vanara were incredibly strong, wielding boulders and tree trunks in battle. The Vanaras were allies of the Riksha, bear-men, and both were created by the gods for the purpose of fighting the Rakshasa. It would be interesting to give Vanara some sort of tag which specifies that they must be at war with another specific civ. I have a read a version which says the capital of the Vanaras was a large cave within a forest, but it seems that it is depicted variously as a citadel or just a region. China has a variation of the Vanara lead by Sun Wukong who found a vast cave behind a waterfall and commanded his monkey-men from there. It would be interested to see a site type which is a more civilized cave or forest than what the elves and kobolds use.
Naga:Naga just means snake, but in legend, Naga characters are given anthropomorphic or straight-up human characteristics. They are depicted as mermaid-like, snake-like, dragon-like or polycephalid. According to legend, Nagas once lived above ground but were chased away by the mighty bird Garuda. Nagas formed two groups, those that live underwater and those that live in the deepest regions of the underworld, which in DF would be the magma sea. In the current version of DF, it would be a stretch to be able to visit cities that are undersea or in magma, but perhaps that will change someday. Perhaps Nagas could live on the coasts and build fortress that extend under the water, or create towers that extend from above the water to below the seabed.
One imagines that the concept of undersea Nagas is somehow related to the western concept of mermaids and to the Dragon Kings of China and Japan, who live in palaces underwater. Some amalgamation of these concepts might be better than using any one on its own.