A lot of fans thought
Paterson Joseph was a sure thing for the Eleventh Doctor and were understandably disappointed by the casting announcement, but as far as I've been able to find out,
the rumour he had been cast originated in fandom itself.
Interview with
Velile Tshabalala, who played Rosita in the Christmas special The Next Doctor.
Interview with
Anjili Mohindra, who plays Rani Chandra in The Sarah Jane Adventures.
On the
Doctor Who Forum (aka OG) in October,
Noma Dumezweni's niece reported that her aunt would be returning to Doctor Who as Captain Magambo, last seen in Turn Left.