It's named a return

Not named just Ivalice
It's named a Return to

On that note none of us Ivalice fans are saying that it will be FFXII Ivalice. What we're saying is that it's related to FFXII and we're happy about it.
For people to keep repeating the obvious (that it's not 100% Ivalice) doesn't really add anything to the discussion.

Since no one knows anything beyond the name we can only guess. My guess is this is the start of viera lore for 5.0 when they add them. Crystal tower and city of mhach are there for us to learn about who? About races/people we didn't understand too well.

That alone implies we're going to learn about new people.........that eorzea doesn't know/understand too well.

These are educated guesses: return, the reasons previous raids where added (to explore to lore of past people/people we don't know), 5.0

Lastly, I think we won't see viera until the third part of return to ivalice which will be close to 4.0's last updates before 5.0. It all goes well together.
I really hope Ivalice moogles become part of eorzea and that we even borrow some of their glamour, weapons and things.