From WoWWiki

Iron dwarves are creatures that can be encountered in the upcoming WotLK expansion.

The Explorers' League has scoured the far corners of the world, seeking to uncover the truth behind the origins of the dwarves. Now it seems they may be one step closer to unlocking the secrets of the past.

The latest clues come from ancient dig sites within the Howling Fjord, where the iron dwarves were first encountered. Etched with runes of power - and with lightning pulsing beneath their thick, metallic skin - they may represent the missing link between the dwarves and the legendary titans of myth. Unfortunately the malevolent iron dwarves have openly defied the Explorers' League and seem intent on destroying any and all artifacts connecting them to the shadowed recesses of history.

Speculation

This article or section includes speculation, observations or opinions possibly supported by lore or by Blizzard officials. It should not be taken as representing official lore!

They perhaps have a connection to the Ironforge Clan, the original clan of dwarves. They may also be an "intermediate" state of evolution between earthen and dwarves. They appear similar to Dark Iron Dwarves, with similar name and the colour of their skin. Due to the runes on their skin, they may be the ones to teach Inscription, or be related to it, similar to how Draenei were linked to Jewelcrafting. This is unlikely however as they are defiant towards the Explorer's League.

Sentient Races and Species
Alliance	Draenei • Dwarf (playable) • Gnome • Human (playable) • Night elf
Horde	Blood elf • Undead (playable) • Orc (playable) • Tauren • Troll (playable)
Azeroth	Ancient • Centaur • Dark troll • Dark Iron dwarf • Dragon • Dryad • Earthen • Elf • Faceless One • Forest troll • Furbolg • Gnoll • Goblin • Harpy • Half-elf • Half-orc • High elf • Highborne elf • Ice troll • Iron dwarf • Jungle troll • Keeper of the Grove • Kobold • Leper gnome • Magnataur • Makrura • Murloc • Naga • Nerubian • Pandaren • Qiraji • Quilboar • Satyr • Taunka • Treant • Trogg • Tuskarr • Vrykul • Wildhammer dwarf
Outland	Arakkoa • Broken draenei • Fel orc • Gronn • Half-ogre • Lost One • Nether drake • Ogre • Ogre mage • Ogre Lord • Rock flayer • Sand gnome • Sporeling
Burning Legion	Annihilan • Ered'ruin • Gan'arg • Man'ari eredar • Mo'arg • Nathrezim • Sayaad • Shivarra • Tothrezim • Wrathguard
Creatures	Beast • Critter • Demon • Dragonkin • Elemental (Air, Earth, Fire, Water, Conglomerate) • Giant • Humanoid • Mechanical • Undead • Uncategorized creature
Miscellaneous	Ethereal • Naaru • Titan • Worgen