Also, Blizzard posted this:
"Scheduled to go live this summer, this feature will allow players to move their characters, within certain restrictions, to a realm of their choosing. This means that player's will now be able to join their friends on other realms without the need to wait for a pre-set mass realm transfer. In addition, this will also contribute to a balancing of the player load from realm to realm, which again is a specific way for us to reduce realm queues and lag. We know that many player's are eager for this service to be implemented, so we'll share further details as soon as more information becomes available. "