This is an incredibly weird idea, but, what if the various civilizations could access new and exciting things over time?
I can even think of ways each civilization could improve. Dwarves could have incredibly strange earthen-based progress, including perhaps adapting underground plants, extracts, and rocks into things. One example I thought of is cave spider venom could be used as a poison in blades and arrows and stuff, as everyone else wants and discusses constantly. Another is that the perpetually cold properties of nether cap could be used in some kind of cool armor or clothing meant to resist dragonfire. A fortress with excess of metals, gems, and all kinds of plants might develop golem soldiers and workers to supplement normal squads and workforces. That kinda stuff.
Humans, meanwhile, would have much more realistic research, discovering new metals (Perhaps having to discover alloys?), new ways to use them, and the likes. Discovering mercury, uranium, titanium, maybe even trebuchets and explosive metal balls launched by them. Obviously no guns or cannons, since Toady already said no to those, but maybe ancient equipment from throughout the globe, like the aforementioned trebuchet, siege towers, chariots, battering rams, and if you want an eastern influence, explosive fireworks, weaponized river boats, and the Hwacha.
Elven "Science" is a bit more... weird. Pretty much, elves would be able to breed animals for whatever, or if we wanna go more magically, combine animals, in ways reminiscent of the Simic from Magic: The Gathering. They would be significantly different with it, of course. Things would have to be connected by degrees of separation. Perhaps they would even have some kind of way to channel the ancestors of whatever they're working with, getting the more primal, formerly extinct versions of creatures in their ranks. This one I don't even think would be considered by Toady, but I myself would mod into a race if possible.
Goblins would be able to use stuff from evil biomes extra well, for example, using Glumprong wood in the production of battering rams, or weaponized bottles of evil fog and rain! Perhaps they could even somehow weaponize undead conscripts made by said evil fog and weather.
Subterranean animal people and kobolds would have much different progress, though. Essentially, they would have access to shamanistic magic. The ability to heal lighter wounds, instill fear and courage, and the likes.
The interesting thing i also thought of here, though, is that inevitably groups take each other's technology, be it through reverse engineering traded goods, sending in spies to other nations, or through reverse engineering equipment after a conquest. Thus, a goblin nation that takes over elves, for example, would have mutated zombies. Meanwhile, dwarves who have taken over a human nation would have amazing things like trebuchet that fling radioactive rocks.
Continuing, technology could also come out of necessity. For example, if Goblins routinely take Dwarven cities through use of evil gasses, the dwarves may end up studying and trying as hard as they can to find some kind of counter, cumulating in plague-doctor styled outfits. If Goblins are routinely beaten by the tough hides of Elven mutants, specifically things like giant arthropods with harder shells, or dinosaurs with thick scales, they may research heavily into better piercing weaponry. But necessity isn't just through enemies. If a human nation is heavily in the desert, they may have better ways to deal with the heat. If there are tons of Goblins on glaciers and tundra, they'd get warmer outfits quicker, and likely equipment better for a nomadic lifestyle, being like the barbarians of old. If a dwarven nation is in smaller mountains, they'd develop more compact workshops, while if they're in larger mountains, they'd perhaps develop better high-altitude equipment, or even more open tunnels for foreign caravans to come to new dwarven sanctums through.
Finally, this would probably need two special new parts of world parameters. "World Research Start" and "World Research Speed." Start would determine how far everyone starts, with the lowest being as we are now, while the highest is everything already unlocked for everyone. Speed would determine how often new breakthroughs are made, with the lowest making a civ lucky to get one new thing in 200 years, while max speed would make new developments constantly come up.
I'm sure some ideas here have already been mentioned, but im sure some havent, for example, the dynamic research.
Below here are more unrealistic ideas; ones that truly channel a modder's insanity.
First up, civilizations researching how to channel raw magical energy from the world around them, perhaps even procedurally generated elemental magic. In one world, the only stone magic might make petrified wood, but in another, earth mages could form pitchblende from the air.
Secondly, war wagons. As in, magical seige weapons mounted on back of wagon. For example, a wagon with a magical ice launcher strapped to it, be it some kinda magical beam cannon, or an ice launcher, or whatever.
Thirdly, juggernauts. In this case, i mean magically powered self-locomoting vehicle sort of seige engines, likely used to slam through closed drawbridges. Perhaps there could even be flying ones used to ignore walls, traps, and other defensive mechanisms.
Fourth, this goes hand in hand with juggernauts, magical power sources. Be it magical flame, thunder, or even the captured essence of ghosts.
All in all, I find all these ideas would give an air of change to the game!