Since the next major update will be focused around magic, a staple of fantasy has not been mentioned by Toady of being a possibility. The Golem. Animated statues of inorganic materials, golems are an ancient concept of robots. Soulless automatons who serve their master without the needs of a human or animal. Dwarf Fortress already has a few creatures made of inorganic substances like Bronze Colossi and Iron Men so this idea isn't out of place to the setting.
Golems could be created by a specific profession tied to magic in addition to a workshop. They need a source of magic to be animated. Either by runes or enchanted mask (depending on what is possible in the Myths and Magic update). Dwarves and humans will use rune-animation while animal men tribes and elves use mask. To prevent golems from being invincible soldiers, if their animation source is destroyed on them the golem will instantly die. Turning into a statue of itself.
Golems can be crafted into generic humanoid shape or certain quadrupeds in two sizes. 70,000 or 1,500,000. No army of Bronze Colossi-sized golems for you. Bigger sizes cost more resources as you'd expect.
Now some ideas of materials golems can be built with.
Wood: Used by elves and animal men as they can't access stone or metal. Players can still build wood golems if they wish but dwarves and humans don't use them naturally. Very flammable.
Clay: Cheap and easy to come by but clay golems are frail. Good for laborer golems instead of combat.
Ice: If steady supplies of ice are your thing, you can build Ice Golems. Don't seem much better than what a clay golem is capable of. Polar animal men tribes build these.
Stone: The most standard golem and stereotypical. Stone Golems will be the perfect go to as they are tough, durable, and heavy. Building one out of a magma-proof stone means magma-immune miners! I can only imagine the increase ease of building magma-based projects with magma divers.
Copper: A metal option that I hope isn't game-breaking.
Other options like Iron, Gold, Silver, or cotton candy have to be researched before becoming available (to your civ or fort specifically) IF these options aren't game breaking in the first place. I was hesitant to include copper for building golems and excluded bronze just in case.
The role of a golem is as automated labor and unliving soldiers for your army. I'm not sure if golems should be intelligent or not so that is up for Toady to decide. How to handle golem's labor ability is an entire debate in of itself so the rest of the thread can figure that out.
Finally I want to end on adding a few creatures related to this topic. treants could return showing up a siege engines for the elves. A subterranean treant could be encountered underground. A sphynx made of sand appear in savage and/or evil deserts. And Iron Warriors, a semi-megabeast that acts like a scaled down Bronze Colossus. In fact, I'll work on these creatures while this thread grows.