6. Tamzin Merchant
One of those changes that would have made a major different to the world of the show, the role of Danaerys Targaryen AKA Danaerys Stormborn AKA Khaleesi was originally intended for Tamzin Merchant, one of the stars of 2005's Pride and Prejudice. After the unaired pilot, however, Merchant left the show - of her own free will or otherwise - and Emilia Clarke was cast in her stead. Merchant went on to do the BBC's Mystery of Edwin Drood while Clarke became something of an unusual feminist role model. Still, it's unlikely that Merchant can hold it against her too much: Clarke was more or less an unknown when she took on the role, as Merchant was when she made her debut in Joe Wright's Pride and Prejudice back in 2005.