Blizzard just announced a feature that they are working on. 5-player dungeons between players from different kingdoms via Real ID. As it is an additional service, the service will be paid.
With the continuing popularity of the dungeon finder, many players have asked for a way to join their real-life friends who play in other realms to participate in rooms together. Today, we want to inform you of the approval of a new feature that is in development process that will allow players to invite friends with Real ID of the same faction to a group without depending on the realm in which they play, and then enter queue for a normal or heroic dungeon for 5 players.
As this is a complex development service, we cannot provide you with a release date yet. It is important that you bear in mind that as with other functions that we offer oriented to connectivity and comfort, some elements of the group system with Real ID between realms will be directed to premium accounts, although only the player who sends the invitations will need to have access to the premium service. As development progresses we will share more details with you; in the meantime, you may see elements of this feature appear in the World of Warcraft PTR.
As you have read, this service will be available to those who have the premium service that includes Auction House and Remote Chat.
What do you think of this feature? Personally, premium services seem fine to me since they are not necessary to play and they add optional improvements that, at no time, represent important improvements for the character but for the fun.