Recently 5th Doctor Peter Davison talked about the possibility of a return to the series to mark the 50th anniversary in 2013.
"I feel no need to turn my back on it, but I don't feel like it's the kind of thing they'd do. I'd be very surprised if they tried to do anything involving the old Doctors because it always takes a slight stretch of the imagination anyway to figure out why the previous Doctors look older - but I'm sure that can be done. But at the same time I'm not sort of longing on it. I'm perfectly happy to have played my part to go back to 'Time Crash'. I don't feel like I'm hanging on a phone call from the 'Doctor Who' offices saying let's do something special."