I'm going to reiterate my longshot, pie in the sky, years old wildcard guess that the Yggdrasil/World Tree we know is there somewhere is secretly an Ancient Kingdom-era space elevator through which we'll wrap up a lot of moon-related longterm mysteries, including but not limited to Enel's return.
This is based on little more than the World Tree/space elevator twist was cool in one of the Xenoblades, and we have to do the moon stuff sometime, so why not here?
Looking forward to whatever Oda does instead.