The world of Gaia has never been more expansive, but something's still missing
For the record, this is not a post criticizing the game or Square Enix. I love Rebirth even with all its odd quirks and glitches that were later patched out. I love how much they've added to build on the characters, their dynamics, their backgrounds, and the ways the world unfolded around them as they went around.
But there was always one niche of this world that the devs have historically avoided: the ancient history of the Cetra and the Summons. I loved the Shinra Theater from Remake and I loved how the Ancient Temple was reimagined. However, I found myself more confused about the brief history around the Cetra's ultimate demise. I understand that it was likely the battle against Jenova in ancient times that weakened them to the point that human factions could fight and defeat them. By the way Ifalna and Aerith were treated in modern times, it's clear their people were practically hunted to extinction over the eras, and we can't exactly fault it as entirely Jenova's doing, though she probably had much to do with it.
However, we have never gotten so much of a hint of what happened to the Summons. Maybe it was just Shinra's assumptions based on historical records that the Summons once lived in harmony with the Ancients (like in FF1). Or maybe the Summons had some ways to remove their presences from the surface of the planet and leave behind materia in their places. Maybe they were forced to leave or maybe they chose to disappear. I have plenty of my own theories and headcanons (I wrote my own worldbuilding for a fanfic, lol), but I wish we had an official answer. Best case scenario would be a FF7 prequel where we play as the Cetra, but I won't hold my breath for one.
Though I grew up with 7, my favorite FF is still 6 precisely because of Kefka that game's world is even further reaching than 7's in some ways. I loved the revelation that the Espers were once living in their own communities before, well, humans got involved. I'd like to see a similar story, or at least some kind of story, with the Summons in 7 too. At least let us know what names or titles they went by back then, other than the "Rulers of the Outer Realms". What are these Outer Realms anyway? How do they fit in with the planet's Lifestream? Are they also part of it?
Honestly, I was hoping to wait for the third game before coming to any judgment, but judging by the most recent interviews with Director Hamaguchi, I don't know if they will be touching on Cetran history all that much anymore. He talked about a lot of other fascinating things (I'm very much looking forward to the new Wutai), but otherwise we may never know. And that makes me just a little sad, but I won't die if we don't. I would like to be proven wrong, though.