The Mirror has today claimed that all 11 Doctors are going to reunite for a special Children in Need scene, during November this year. My first thought was: "Isn't the 1st Doctor sort of... dead?" (Obviously, no disrespect there...) But apparently, they are going to superimpose the first three Doctors, using special technology.
An 'insider' said: "This is a momentous episode for all Doctor Who fans. Never before have all the Doctors been in the same room, let alone in the same show. The script has already been started and it’s classic Doctor Who - really witty and very sharp. Viewers will see the Time Lords regenerating and emerging one by one from the TARDIS, each with their own quirky opening line."
Well this all sounds very interesting, but it would take a lot of work, and please remember it hasn't yet been confirmed by the BBC.
Thanks to WhovianNet for the information.