8.0 speculation

[Yuella]

I think what we'll end up doing is transport the inhabitable part of each reflection (along with the people) to the source and then destroy the reflections. So we'll have Treno from the 9th, Norvrandt from the 1st, Zero's domain from the 13th and the floating islands from the 4th (plus whatever is left in 8th and 11th) in the source.

[Cilia]

I think what we'll end up doing is transport the inhabitable part of each reflection (along with the people) to the source and then destroy the reflections. So we'll have Treno from the 9th, Norvrandt from the 1st, Zero's domain from the 13th and the floating islands from the 4th (plus whatever is left in 8th and 11th) in the source.

That's the same thing Calyx did with the Key, on an even grander (and messier) scale.

Not to mention the fact Norvrandt occupies the same geographic space as Eorzea on the First, and there are other cities on the Ninth left other than Treno we don't visit.

It's not a forthcoming option based on what we have and know about the protagonists, and even if it were there are serious logistical issues on top of the rejoinings still bringing elemental Calamities to the Source.