Players on connected severs will be able to join the same guilds, raids, dungeons and more. According to the announcement post on Battle.net. the feature is intended to help players on lower-population realms "group up, compete and connect" with more players in order to tackle the game's more challenging content.
"As WoW has evolved, we've seen players naturally gravitate toward a subset of very active realms, leaving behind lower-populated realms," the post reads. "Due to the massively multiplayer nature of World of Warcraft, certain kinds of gameplay experiences simply aren't well-suited to a low-pop realm. By allowing players from two or more lower-pop realms to play together, we hope to give more players more opportunities to participate in group-oriented activities, helping to foster a more vibrant in-game community."
The post adds that by connecting servers, populations can be linked in a way that's not disruptive to players and won't impact their "sense of identity and character." If Blizzard were to simply merge servers, character names would be lost or duplicated, resulting in confusion.
Specific realms have not yet been selected for the feature, though only realms of the same type — Players vs. Player, Player vs. Environment, etc. — will be linked.
"There should be no limitations," the post reads. "We want the experience to be seamless, and we expect it work as if you're suddenly part of a much more active realm. We haven't yet determined when we'll be creating the first Connected Realms, but we expect it will be some time after the launch of Patch 5.4."