I feel that, even if worship of the Phoenix Witch is the most prominent display of killjoy spirituality and religion, there must be a diverse samplings of religious practice in the zones.
This could range anywhere from already established religions that were either prominent in battery city or have been passed down through the generations, to certain gangs starting to revere just, one particular rock and it just grows out of proportion and now there’s a hundred people worshipping a rock and no one really knows why. (This could take the less humorous form of killjoys really devoted to a dead friend spreading around stories and devotion to a dead friend to the point that that person becomes a religious feature)
There’s also a possibility of a pantheon that exists around the Phoenix witch. She seems mainly to be a goddess of death and the afterlife, and whether there be one other figure who contrasts her in representing life, or an entire group of gods and goddesses presiding over anything from music to the sky
There’s just a lot to talk about here and I think that, because of the focus on individuality in the zones, basically any theory about killjoy religions could coexist, and it would be interesting to see how they interact with each other