In 2003 a blue post on the World of Warcraft Forums revealed a breakdown of the progression of future game regions, but was later removed from the site.  Before the post was taken down, its content was recorded and has been circulating the internet creating all sorts of new rumors.  I’m not going to take a position as to whether I believe this information is true or not, but a lot of the information does line up with what has happened with the progression of World of Warcraft and it’s subsequent Expansions:

Draenor Set

Azuremyst Isle – 1 to 10
Bloodmyrk Isle – 10 to 20

Eversong Forest – 1 to 10
Quel’thalas – 10 to 20

Hellfire Peninsula – 58 to 62
Zangarmarsh – 60 to 64
Terokkar Forest – 61 to 65
The Deadlands – 63 to 67
Nagrand – 64 to 68
Blade’s Edge Mountains – 66 to 70
Netherstorm – 67 to 70
Shadowmoon Valley – 69 to 70

Northrend Set

Borean Tundra – 67 to 70
Howling Fjord – 67 to 70
Dragonblight – 69 to 72
Grizzly Hills – 70 to 73
Crystalsong Forest – 72 to 75
Zul’drak – 73 to 76
Sholazar Basin – 75 to 79
Storm Peaks – 76 to 80
Icecrown Glacier – 78 to 80

Maelstrom Set

Gilneas – 77 to 80
Grim Batol – 78 to 81
Kul Tiras – 79 to 82
Kezan – 81 to 86
Tel Abim – 83 to 85
Zandalar – 84 to 87
Plunder Isle – 86 to 88
The Broken Isles – 87 to 90
The Maelstrom – 89 to 90

Plane Set

Pandaria – 1 to 10
Hiji – 10 to 20

Wolfenhold – 1 to 10
Xorothian Plains – 10 to 20

The Green Lands – 88 to 91
The Dying Paradise – 91 to 94
The Emerald Nightmare – 94 to 97
The Eye of Ysera – 97 to 100

Legion Set

K’aresh – 96 to 99
Argus Meadowlands – 97 to 100
Mac’Aree – 99 to 100+
Maw of Oblivion – 100++
The Burning Citadel – 100+++