I found this tidbit over at Kasterborous. They are saying in a interview that the 5th Doctor Peter Davison would be happy to come back as The Doctor in a 50th Anniversary Celebration. He was quoted as saying
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 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.
Well lets hope they do something with the past Doctors even if it is for Children In Need or something. Well we can keep our fingers crossed.