Dom Pedro II
Modder For Life
Ok, I've got an idea... I wouldn't want these religions in the game if they're just there to be pushed aside by what we might call full religions. With that said, I think "minor" religions ought to be modifier religions. By this, I mean that they exist in a civ abstractly... through buildings etc., and then when a religion is founded in their civilization, these modifier religions modify the big religion.
So, for example, the Aztecs have a minor religion that involves ritual sacrifice. If they found Buddhism, Buddhism becomes a religion with human sacrifice. For the Mayans, they incorporated a lot of astronomical features into their religion, so if they found Christianity, astrology will be an important aspect.
What do these things actually change? I don't know. New idea...
But it's something to consider.
EDIT:
Thinking it over some more, this would be a good way of removing the interchangeability of the different religions without having to actually go to the length of actually making them inherently different. Rather they would inherit specified traits of the civilization's culture. So converting to Taoism from Buddhism would have different strengths and weaknesses, but those strengths and weaknesses would be defined by who founded those religions and not as part of some built-in difference between the two.
I think this is important since, as a modder, you want to reach the maximum audience possible and offend the least number of people possible without compromising your views and beliefs, and when you make one religion spread faster or deny them health benefits from certain kinds of prohibited food, or have them build units like Jihadi or Crusader or something, you put yourself at risk for criticism from people who think it's inappropriate or inaccurate. So with this, you can minimize that... but that's not the major benefit. More of a side one...
Also you don't have to come up with ridiculous names like Cult of Quetzalcoatl or Greek Pantheon, etc. etc.
And lastly, it makes things more dynamic and would help prevent beelining to Religion X because it provides this benefit or that benefit.
So, for example, the Aztecs have a minor religion that involves ritual sacrifice. If they found Buddhism, Buddhism becomes a religion with human sacrifice. For the Mayans, they incorporated a lot of astronomical features into their religion, so if they found Christianity, astrology will be an important aspect.
What do these things actually change? I don't know. New idea...

EDIT:
Thinking it over some more, this would be a good way of removing the interchangeability of the different religions without having to actually go to the length of actually making them inherently different. Rather they would inherit specified traits of the civilization's culture. So converting to Taoism from Buddhism would have different strengths and weaknesses, but those strengths and weaknesses would be defined by who founded those religions and not as part of some built-in difference between the two.
I think this is important since, as a modder, you want to reach the maximum audience possible and offend the least number of people possible without compromising your views and beliefs, and when you make one religion spread faster or deny them health benefits from certain kinds of prohibited food, or have them build units like Jihadi or Crusader or something, you put yourself at risk for criticism from people who think it's inappropriate or inaccurate. So with this, you can minimize that... but that's not the major benefit. More of a side one...
Also you don't have to come up with ridiculous names like Cult of Quetzalcoatl or Greek Pantheon, etc. etc.
And lastly, it makes things more dynamic and would help prevent beelining to Religion X because it provides this benefit or that benefit.