The concept art shown there is most likely the new Viking race called the Vrykul that lives up in Northrend. They'll be featured in the first 5 man instance at Howling Fjord called Utgarde Keep. I'm really looking forward to seeing a lot of original content and lore this expansion since there really is not much known about Northrend to date.
A tiny snippet of information on the Vrykul from WoWwiki states: "Utgarde will be inhabited by the Vrykul, a Viking-like race bent on proving their strength to the Lich King, who will raise the most worthy of their warriors to serve him beyond the grave."