I hope the Master comes back. He is a much ore intriguing villain than the usual suspects (Daleks, Cybermen....). Though, would be fun if he came back a friend rather than enemy now that the drumbeat shoukd have stopped.
I had this idea back when he first came back. At the end of "The Last of the Time Lords" when the Doctor wanted to take the Master with him, I thought that woukd be the most awsome pairing ever. The Master is one of the few characters who can stand as the doctor's intellectual equal. While many companions have had qualties or skills that made them able to lookout for themselves, they've never really been an equal. It usually like a reacher student/ or guardian/ward kind of relationship. But travelling with someone on his level would be a new dynamic and something I'd like to see.