What are some of your fun theories about FFXIV's lore?

Mine:

Tataru is one of the missing ascians that is sympathetic to our cause.

We never left the place we battled the Endsinger and Zenos. Our remote didn't come back and DT and everything after is just our WoL hallucinating while slowly going mad as they quietly starve in a void with Zenos's corpse.

All the reflections are being reabsorbed into the source at an ever increasing speed and one day, after growing aetherially stagnant and suffering a series of minor calamities caused by the ever shrinking aether pool, they will just quietly disappear.

With a large number of unsundered souls now back in the lifestream, Etheirys is going to see an emergence of highly skilled wizards that can manipulate aether in such a way that they will be heralded as gods amongst men.

With Zodiark and Hydi gone, Ultima will reveal herself to be a being of Dynamis. She will use Metion and her sisters, who were created due to Ultima subtly influencing Hermes, as her own Ascians and continue to try to restore the shard and bring her own pieces back together.