That casting speculation
(bumped up from a comment to sinclair_furie)
I am not hugely surprised. It is well recorded that Peter Davison, who was the last Doctor apart from Ecclestone to choose the time of his leaving the part, talked to Patrick Troughton as he started filming, and that Troughton told him to do it for no more than three years. It is also well recorded (even before last month made it effectively canon) that Davison is Tennant's favorite Doctor, and that he visited the set to talk to Tennant shortly after filming started on Season Two. It would be pretty astonishing if Davison had not passed on that piece of advice (though Tennant, as a big fanboy himself, presumably already knew about it).
Having said which, of course it has not really been confirmed yet.
I am not hugely surprised. It is well recorded that Peter Davison, who was the last Doctor apart from Ecclestone to choose the time of his leaving the part, talked to Patrick Troughton as he started filming, and that Troughton told him to do it for no more than three years. It is also well recorded (even before last month made it effectively canon) that Davison is Tennant's favorite Doctor, and that he visited the set to talk to Tennant shortly after filming started on Season Two. It would be pretty astonishing if Davison had not passed on that piece of advice (though Tennant, as a big fanboy himself, presumably already knew about it).
Having said which, of course it has not really been confirmed yet.