This risks veering the thread wildly off topic, but:
I think the example's you have in the OP would work better as cultures/subcultures but I think this concept would really work to explore some of the more out there things from prev games we can't quite make from current modularity options (I also feel that these shouldn't be form-locked):
AOW2 draconians had varied bodies, winged humanoid, humanoid fire breathers & a big, ogre sized melee unit.
AOW2 shadow demons had a a ton of unique designs, but I'd base this more on the kir'ko, the standouts for me are: Barrager, Ravenous & Engulfer.
AOW3 frostlings had a mixure of small dwarfy/goblin type figures, alongside tall, more elegant figures with more frost witch ancestry as part of the same race.
AOW3 tigrans had the sphinx as a racial unit.
Mechanically, these would work the same way mount traits do with "Optional Cavalry") units, applying different visual and mechanics modifications to specific units.
Each bullet point could also be split into its own trait for even more modularity, but I'm keeping them grouped here for ease of reading: