I think these worked well in a semi-historical background with sims medieval. But I think the modern day environment in sims 4 is too similar to real life to add in made up religions. I think a lot of players have very different views from one another to find a way to implement them for all.
For some it will be too close to real religions while for others it won't be close enough because they want actual existing ones.
If this would ever be added, I think it is unlikely, then it should be a new free pack like the holiday pack so players can choose if they want to use it or avoid it.
Now I feel like playing sims medieval again. Lol. In that game peteran and Jacoban religion fit in very well.