The blog, Planeswalker's Stronghold has a sketch signed by Magic artist Daarken and it is clearly of Sarkhan Vol. Brainstorming the story folks have suggested that he might be making a reappearance in Rise of the Eldrazi and if this artwork is to be believed, he will be.

Update: The art is from the tutorial by Daarken found here. It is NOT of Sarkhan Vol and is for a character he calls 'Nibru.' This does not however disprove the rumor of Sarkhan Vol being IN Rise of the Eldrazi.