In the upcoming 5.4 Patch for World of Warcraft, Blizzard will connect low-population Realms to increase player count to encourage players to take on larger challenges like Dungeons or Raids.
The connected Realms won't rid of a player's home Realm but instead connect them. You won't see an immediate indication to indentify which Realm a player comes from, but you will see the Realm when in chat. As for which Realms will see a connection, Blizzard remains undecided. PvP Realms and PvE Realms will however not connect with each other.
We found out just last week World of Warcraft's continued decline in subscribers that totaled another 700,000 users. The drop brings the total count down to 7.7 million users as opposed to its peak at over 12 million users.
Blizzard also recently added microtransactions to World of Warcraft which could indicate a possible move to free-to-play. With the largest install base among MMORPGs, a move to free-to-play seems unlikely. If users continue to fail to subscribe however, expect some change.
For a more detailed questions and answers, you can read Blizzard's blog post explaining the connecting of Realms.
