In DF Talk #28, Toady brought up "[adjective] dwarves" as a creature variant originating from mythgen.
The example of cloud dwarves and cloud dragons is a strong example of a shared spherical association. There's a pretty strong cultural background of what a creature associated with the sphere of SKY would be. Power of flight (either innate or as a spell), tissue layers could be given air-themed colors like sky blue or clear, any other interactions they can access would typically be either centered in the sphere of SKY or allowed to trickle in from related spheres.
1. "Cloud dwarves" seems like a question of making the data structure for creature/object variations robust enough to have spherical and arbitrary tagging. Will we see the raw-defined creature variation object be expanded to serve the purpose of mythically-directed randomness in this way?
Like the idea of a single variation comprising [CE_ADD_TAG:CAN_SPEAK] + [CE_ADD_TAG:SKILL_LEARN_RATES:SPEAKING:200] given the sphere of SPEECH, when a creature is speciated to fit the magics of the speech domain. Likewise, different "dragon" abilities and bodies could be stored in the creature variation file with the creature definition calling those, in a way that the world options can briefly look at the creature files to make buttons for.
Perhaps some way to discriminate variant generation by creature tags, that way we don't get redundant silliness like "talking dwarves" and "dark goblins" that describe what they already do. "Bardic dwarves" sounds more apt for an already-speaking creature and is more a flavor matter, but unless the concept of a goblin in DF is reworked to not always originate from dark pits there's not really any meaningful separation between a dark goblin and a banally evil regular goblin. Likewise, you'd need elves that don't live in forests for "wood elf" to be a meaningful discriminator, etc.
2. Will we see the entire concept of a religious sphere also become opened up to modding?
I know sub-domains of ANIMALS was talked about, but the idea of adding new spheres seems like something modders could do easily if the data structure was editable. The god descriptions and language symbols, and hooks in the code to link them with forces and spherical variants.
3. I'm interested in the "humans, and one to two other things" scenario because it means worldgen-relevant procedural entities to elevate certain types of creatures. There are plenty of intelligent creatures already with well-defined associations, how might that be reflected when the game gets around to generating an entity definition for them?
Satyrs love music and parties, gnomes can go in both really dwarfy (the tinker archetype) and really elfy (mushroom houses/"underground wood forest retreat") directions with that Paracelsian link to earth, and animal people should at least pay lip service to their ecological niche (diet and biome primarily). Gorlaks are described as good, so it'd be unusual having them originate a cruel and selfish civilization.
We also can sorta expect spherical associations to loop back around from flavoring original entities to modifying vanilla ones in the same way. Dark elves, if they're more broadly embodying the concept of evil rather than benign non-illumination, would behave in a certain general way. We'd expect them to dwell in cavern layers and dark pits, use evil words in their names, enjoy cruelty and hostility, just basically follow the goblin blueprint. Not all entity changes are created equal, as I'd imagine fire dwarves might be more passionate and prefer settling in warm biomes, but the subspecies is similar enough to integrate with the mountainhome unless there's a cultural rift with ice dwarves.
(edit: removed some further technical ramblings about implementing object variations in relation to mythgen)