Honestly it depends on how well they write the two games you mentioned just suffered from bad writing in general. Oh my idea is within the bounds of the FFXV lore, it just focuses on the gods more on how they are probably outside the bounds of the earth of FFXV
It's really just using this line
"Mysterious beings create
Eos. The
astrals participate in the world's creation and become gods themselves"
"The mysterious beings retreated from the world, while the Astrals would remain - in future years, they would become recognized as a race of their own, with their own language and agendas, and a wish to protect the natural world"
It's really just fleshing out these mysterious beings that fled, and using these mysterious beings as something related to the FNC like fal'Cie or something.
It's really this:
The Astrals would remain the same, The Mysterious beings that are clearly outside the earth of FFXV would appear, Etro would be seen, and events of earth's history would be somewhat different, the lore of the gods would be expanded upon, but the earth would be somewhat different.