Why DIDN'T Eph get sent far into the future?
Probably because he didn't want to. He just used the Lifeboat to survive the destruction of the world and then rebuilt so the others would have somewhere to return to. Might even be in the Book of Prophecies.
If no one stayed to rebuild Daybreak Town into Scala then the legacy of the Keyblade would probably been lost unless Luxu took into his own hands to do so, as there is no mention of the MoM anywhere else in story while it's stated by Sirgurd that Ephemer was the first Keyblade Master.
.. Which leads us to another problem: Ephemer is know as the first Master, so no one knew about what happened before. The way Sigurd talks about Brain makes it pretty clear he never mentioned the other Dandellions, much less the Foretellers who came before. It's understandeable from a narrative standpoint if Ephemer didn't want people to find out about that tragic outcome and go looking for Lux again, but it gets confusing when we think about Xehanort.
The whole fairytale Kairi heard from her Grandma still works, though, as children rebuilding the world with the light in their hearts is still coherent and it doesn't mention keyblades or anything.
The thing is, Dark Road is still unfinished, and now that we know Time Travel is a thing, everything is open. We have to treat UX ending as the canon flow of events but a lot can happen in the next updates.
I don't think we'll get an actual retelling of the whole timeline, but we should keep in mind that this is only one side of the story.