The most server-efficient way to do it is actually the opposite of a transfer. It's simply to have the whole character database stored in every server, so what changes is simply what server your client is connected to. Then, when you switch world again, updated data of your character is sent to all the other servers only once.
How is this efficient? A copy of every character ever created on every server? You're joking right?

One thing you fail to realize is that just because the servers need to talk to each other for the content finder, it doesn't mean that transferring characters from one server to another is feasible. They specifically said that the content finder would be to create an "instance" of the dungeon or w/e content you and your group are doing. This is not even close to the same thing as a server transfer. It's a localized instance of one particular zone with at max 8 people in it.