(Entire MSQ Spoiler Below)
At the very end when we talk to the Scions before splitting up, Y'shtola expressed a desire to write a book regarding everything that we've learned during our adventurers in Eorzea, the First, and the edge of the universe. I was thinking that we have basically gleaned some pretty earthshattering truths about reality and our world that might be dangerous for the average person to know if the writers wanted to explore that route.
IRL religions in part seek to answer the unanswerable - how things came to exist, what happens after life (if anything at all), why do we exist, what is our purpose, morality, etc etc. Seeing the impact of the truth behind the Dragonsong War had on Ishgard and its Church, wouldn't revealing the truths behind the Ancients, Ascians, Hydaelyn, the Aetherial Sea, Ultima Thule, or even the heat death of the universe (from the Ea) have huge consequences on the average person realistically?
We essentially know our "gods" or "creators" (the Ancients) and the ultimate fate of different civilizations that have reached the "zenith" of their due courses (Omicrons and conquest, the Ea and knowledge, the Freedom society and unification, Ra-La and hedonism). We also literally know what happens after death and that Sharlayans have a potential portal to talking to your loved ones after death. There is also the fact that we are literally "broken" beings that were once godly, with fractured versions of ourselves existing in other dimensions.
Wouldn't people want to literally meet their "other halves" on the other shards? Or see their departed loved ones? Or seek to glean knowledge and technology from the Ea or Omicrons in Ultima Thule (since we can seemingly teleport there)? Or bring back the "true creators" (the Ancients)? Or kidnap the Loporrits for personal gain?
Or fear/worship the WoL for killing "God" or being the closest thing to a god? What about persecute the remaining Garleans out of fear of the potential of magitek and Black Rose, knowing they literally doomed an entire alternate timeline? How does Magnai feel knowing that we are his daddy/mommy (Azim/Azemya)?
Reminder that we chose to keep the truth behind Bahamut and the 7th Umbral Calamity a secret because it might be disastrous for people to worship the pheonix/Loisoix.
Even if Y'shtola decided to not publish a book, I think there are enough random NPCs across the MSQ that can piece together some damning truths. I think everyone in Sharlayan at the end knew a great deal about the Ascians, Final Days, Hydaelyn, and Meteion. Surely the people who donated Allagan tech were somewhat aware of the reason why we needed adamantite to travel to the edge of the universe.
I can totally see multiple cults or new religions forming up due to these revelations. Some interesting food for thought I think.