This is going to be every time now, isn't it?
Its the last day, the final frantic hours of speculation before we find out who the Thirteenth Doctor is going to be and I thought I was going to get through it without seeing that rumour come up again. You know the one: the “David Tennant is coming back” rumour. Its not such a mainstream thing as it was when Smith was leaving but there do seem to be convinced that not only is the only thing that can “save” the show being the return of Tennant but that it is actually going to happen.
And I don't mean that in some way that involves a complicated in-universe explanation about regeneration. The process of regeneration is pure plot fairy dust, it works however the production team want it to work. Hell, it wasn't even until the third time it happened that the series even decided it was a thing Time Lords naturally did.
It has nothing to do with that.
It has everything to do with the fact that David Tennant is an actual guy with an actual career and he isn't going to take the massive backwards step (and massive pay cut) of returning to a role he left eight years ago. Generally speaking that's something actors only do when they've got nothing else on, with apologies to the cast of Girl Meets World. Yes, he's reprised the role for Big Finish but a) that's ultimately a week or so's work at a time and, b) probably not something the BBC would have signed off on if he were going to be the “current” Doctor again.
And think what it would mean for Chibnall to come in to the showrunner role and his first announcement is that no one he could cast would be as good as just bringing back the series' former star. He'd basically be declaring that his own vision of the show is to be nothing more than a tribute act to a previous version of the show. No showrunner in their right mind would do that.
But I bet we'll be doing this same thing in three or four years when Thirteen is on his (or her, fingers crossed) time comes.