I am positive that Elspeth will appear once again as W. She may be multicolored with something other then W but Theros appears to be mostly mono-colored so I doubt it. As for the other Planeswalkers I speculate that Dack Fayden will be one of them. I assume he will be U, but it's me being baseless. The third Planeswalker hopefully will be multi-colored with W G since this combination has not been done before with Planeswalkers.