Early this morning our staff uncovered pictographic evidence of the Celestial Steed and Lil' XT Pet being sold soon at the Blizzard Store. The image is no longer in their front page rotation, but likely it won't be gone for long.
We don't know any details. That's all there is to say on that. So any speculation about price, functionality, etc... it's all just that. Speculation.
We do know, however, that this is the first mount being sold at the store; and the first useful in-game item you can directly buy with real world money (if you don't count the mounts from the WoW TCG game).
Video of the steed after the break.