Low chances of happening: I would like religions to be not controlled from HQ in the underground bunker under your palace, but phenomenons being born somewhat independently of civilizaitons' agency, and then civs having to choose what to do with them, adapt to them, reshape them to their needs, stomp them out etc. Low chances because it would essentially require turning the entire 2012-2025 religion system upside down and redesigning it mostly from scratch. I also think Firaxis would say "no, it's crucial for dopamine shots into the vein that the player personally designs religion", even though I genuinely think this alternate approach could allow much deeper, more strategic, more interesting religious gameplay.
Slightly higher chances of happening: I would like religions to be much more structurally varied - so
not every religion is Christianity/Islam style "hurr I have prophers and this is my state religion and I send missionaries from my capital, wanna convert the entire world, all other religions should disappear" etc.
So you could also:
- Be perfectly fine and benefit from converting to already founded, culturally alien religion, and still have agency in reshaping it to your need (IRL: all the time everywhere, most obviously with Rome and Christianity or Iran and Islam)
- Found two religions, with this option having benefits and drawbacks like dual classing in RPGs (IRL: India, China)
- Syncretise different religions, make them blend into one another (IRL: African religions and Islam/Christianity)
- Be perfectly fine with several religions coexisting in your empire, with some limitations (IRL: Rome)
- Have religion spreading only culturally/politically, with no prophets or missionaries (IRL: Confucianism, Taoism, Hinduism? Zoroastrianism??)
With special sort of bonuses to compensate for that
- Be perfectly fine with keeping your old style pagan pantheon, which is usually clearly inferior option but sometimes it is good option thanks to the special set of strong nature-, tile-, resource- focused bonuses of your ancestors
- Have non-proselytysing religion, akin to Judaism, focusing instead of spiritual mastery of the chosen people (the problem: in civ7 civilizations can't stand the test of time like Jews did

)
- In the modern era get to choose between fundamentalism, state religion, secularism, and state atheism (with the latter enabling you to have anti-missionaries converting people to atheism, sort of like Communists did with more ro less success)