Instead of merging low population servers Blizzard has decided to try something a little different by introducing Connected Realms.
Connected Realms sees servers joined together to share population and resources, but still retain their individual identity. Basically the servers will remain independent, but share population, a single auction house, and players from both sides can group up, join guilds, and PvP together.
“Other alternatives such as merging realms would require us to force character name changes if there were conflicts, and could lead to confusion for returning players who’d log in to find their realm missing from the realm list. Some players also feel strong ties to their realm’s name or history, and we don’t want to erase that,” the developer explained.
This new feature will go live with patch 5.4.