An unofficial Leak of the Ultralisk Unit. Looks killer! It has been confirmed by Blizzard official Karune!

Karune: "Nice find ;) This IS the new Zerg Ultralisk and you will be learning more and seeing more of it relatively soon. Also, the purple coloring shown on the Ultralisk's back are team colors and will change change accordingly."

Hear that? he said Relatively soon :) Anyway here is the picture from WoW Insider where it was first leaked:

Src: WoW Insider