It has been mentioned before[1] that divine spheres will be customisable to some extend via the Mythgen params/editor. Does it stop there?
Reading off what I think you mean for Toady's reply, probably similarly to exposing FB's generation, parts of it are too embedded in to code (running stringdumps for data you can't re-use for instance) with not a lot of room for tokenization ; which got centralized, you can build your own FB's, Werebeasts, or Clowns and overlap them to replace the randomized ones, but this is still finnicky modding subject.
So when we might get a sphere with some token specification after the map-rewrite, it might be simple enough to document as we can already see with temple designs alternating through spheres related to dieties, dictating the kind of tokens for biome that a non-copy paste fantastical area-map would require (
as that is the only thing outside of soil and populations that is static, and a more likely avenue for pursuing your question), then let the sphere run its course into interpreting that information, and really i dont think for a while we'll be able to inference more information behind this.
And the Mythgen uses this random-gen or input information, but it'd probably just work without mythgen as being "just there" with less intermediary details like the HFS, to randomize aspects of it like clown reincarnation/intelligent mortal afterlife stuff.