Blizzard just posted a teaser image on the World of Warcraft Facebook page of a winged lion mount that will be coming soon to the Blizzard Store. No further information has been released, so we don't know how much it will cost or when it will be available. As a comparison point, the Celestial Steed mount is available through the Blizzard Store for $25.
Wowhead recently posted an unfinished 3D model of the winged lion mount that was found in the patch 4.1 files. Check it out to get an idea of what the mount will look like in-game.
Even though we don't have any details yet, would you buy this mount when it's released? Do you own the Celestial Steed?