Living Steel is being introduced in the Mists of Pandaria expansion. No one knows what it will be used to craft yet but it most likely will be for the high end items. Living Steel is the new Truegold, which was used in a lot of the high end Blacksmithing Recipes, with the occasional Jewelcrafting and Engineering use.
Alchemists are already preparing to Transmute: Living Steel as there will surely be a high demand for it. If you’re looking for a gold making opportunity, it is advised that you look into leveling an Alchemist now to make Living Steel, at least for the beginning of the expansion.