They did it a whileback; basically you put an app in on the lodestone saying which server you wanted to transfer to; there were a few to choose from.
SE would then do the transfer at a later date during a maintenance, it went really smoothly! The only downside was that there was limited space per server so some people couldn't go where they wanted.
I see this transfer going down the same way but with fewer space restrictions (hopefully) because a lot of players (not all) are going to move to a datacenter close to them, which will open up space for people to move about
Fingers crossed for a smoother transfer process! haha