In 2003 (before WoW went live) Blizzard supposedly posted this list of the gameplan/outline of all zones/expansions up to level 100. So, make of it what you will!
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- 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

Deephome - 88 to 91
Skywall - 91 to 94
The Abyssal Maw - 94 to 97
The Firelands - 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+++