A few days ago, Blizzard posted that there will be free migration for characters:

The following Free Character Migration will be available from November 26th to December 2nd:

Al’Akir => Dentarg, Xavius
Argent Dawn => Darkmoon Faire, Steamwheedle Cartel, The Sha’tar
Burning Legion => Ahn’Qiraj, Daggerspine
Crushridge => Bladefist, Karazhan
Drak’thul => Burning Blade, Deathwing
Grim Batol => Dentarg, Xavius
Magtheridon (Horde only) => Zenedar, Haomarush
Neptulon => Ahn’Qiraj, Daggerspine
Outland => Bladefist, Karazhan
Ravencrest => Burning Blade, Deathwing
Sylvanas => Auchindoun, Lightning’s Blade
Twilight’s Hammer => Auchindoun, Lightning’s Blade

However, there are a few realms that have been very busy lately due to the migration such as Argent Dawn. The migration is for a new realm known as Chambers of Aspects so this is a great opportunity for you to change the environment and enjoy a new game in a new realm.

It is available until December 2 so be sure to take the chance if you have wanted to start in a new realm.