Existing religions are less scriptural you seem to be assuming
I will argue that religions going forward will not look like the great religions of before (great meant strictly in the sense of having a lot of followers or influence). Already in the West we underappreciate the differences between the familiar religions (i.e. Christianity, Islam, and Judaism) and those of other parts of the world. Those three religions are inextricably linked to each other through their origins, and there is a reason that they are commonly conceived of as 'Religions of the Book.'
But away East, Buddhism doesn't really have a comparable corpus of divinely inspire tomes (not least because they don't have a comparable view of divinity of Godhead). The same can be applied in varying ways to the other well-known or well-followed religions of the East. I am not a follower, student, or expert of those religions, so I will decline to comment further on exact differences; but suffice to say, the centrality of Scripture in the Religions of the Book is different from other religions in the world.
Modern 'religions' won't look at all like the old kind
(HEAVY CONTROVERSY WARNING !!!!!)
Do you believe in global warming? Why? Some scientists published some studies about it. They have all this evidence that the world is heating up and that this is going to be a disaster for humanity and the Earth. Can you explain to me in detail why their argument is true or do you take the scientists on....faith?
Do you think that people who oppose gay marriage should not be allowed to speak at public events? I mean, that is definitely mean-spirited, and it oppresses those who are gay by denying them basic rights. What is the justification for believing that gay marriage should be available to all? The moral justification is the Golden Rule, say many. Why is the Golden Rule 'true'?
Here is the point: If you believe in global warming, and I tell you that global warming is a hoax; or if you believe in gay marriage and I tell you that gays should not be allowed to marry, you will likely be offended. How is your reaction any different than if I told a Christian that Jesus was a con-man or told a Muslim that Mohamed was a pig?
Given the great variance in religious practices among people around the world, what is religion other than a set of commonly held beliefs held on faith? Belief that taxes or communism or government is bad, that global warming is a threat, that personal sexual freedom is good, or that anti-trans or anti-Black Lives Matters attitudes are a crime are basically that: tenets held on faith. The belief in a 'God' figure isn't really a central concept of religion, Abrahamic bias notwithstanding. Again, I am no expert, but if you take a look at Eastern religions, or even the familiar pagan polytheism of Greece or Norseland, the idea of an omnipotent god is not really that common.
We have no rigorous evidence that taxes are bad, or that anti-trans people are evil, and the great majority do not have or do not understand the evidence that global warming is real. Therefore many of our strongly held beliefs have the character of religion.
To answer your question then: is there a 'Bible' of global warming or a 'Koran' of gay rights? No, there is not. There is simply a set of mutually reinforcing social messaging on the topic, that spreads orthodoxy and fights heresy. You can get your modern religion through any communication medium out there.