We've seen the Doctor condemned to enforced regeneration before- the final act of The War Games preceding a change of face for his Second incarnation...
While that in itself is radical in that the Time Lords passed sentence after he had done what he deemed right- calling them in to assist in returning the various soldiers of the War Zones to their rightful places in time- perhaps even more of a surprise is that he gets no say whatsoever in the process of choosing his next appearance, albeit after rejecting every single choice from a specially prepared selection! Lets have a look over proceedings once more, shall we?
DOCTOR: Now then, what about me?It opens up a world of possibilities for a future Doctor/showrunner. Apply a little lateral thinking, especially in the light of the Master's recent post-regenerative sex change- which might have come about by similar means, & the chance to potentially condemn a new incarnation of the man known as 'The Oncoming Storm' to a new start as a woman!
TIME LORD: We have accepted your plea that there is evil in the universe that must be fought, and that you still have a part to play in that battle.
DOCTOR: What? You mean that you're going to let me go free?
TIME LORD: Not entirely. We have noted your particular interest in the planet Earth. The frequency of your visits must have given you special knowledge of that world and it's problems.
DOCTOR: Yes, I suppose that's true. Earth seems more vulnerable than others, yes.
TIME LORD: For that reason you will be sent back to that planet.
DOCTOR: Oh, good.
TIME LORD: In exile.
DOCTOR: In exile?
TIME LORD: You will be sent to Earth in the twentieth century, and will remain there for as long as we deem proper, and for that period the secret of the TARDIS will be taken from you
DOCTOR: But you, you can't condemn me to exile on one primitive planet in one century in time! Besides, I'm known on the Earth. It might be very awkward for me.
TIME LORD: Your appearance has changed before, it will change again. That is part of the sentence.
DOCTOR: You can't just change what I look like without consulting me!
TIME LORD: You will have an opportunity to choose your appearance.
DOCTOR: Oh, well, that's not so bad. But I warn you, I'm very particular.
TIME LORD: Here is your first choice.
(A man with a big bushy beard, followed by other sketches.)
DOCTOR: Oh he's too old! Well he's too fat, isn't he. No, he's too thin. That one's too young. Oh now, that won't do at all. It's ridiculous.
TIME LORD: You're wasting time, Doctor.
DOCTOR: It's not my fault, is it? Is this the best you can do? I've never seen such an incredible bunch.
TIME LORD: Since you refuse to take the decision, the decision will be taken for you.
Of course the Doctor had also been on trial five selves after his encounter with the War Lord, so this would not be entirely new territory.
We also know now better than ever that a change of gender is an option, as first established in The Doctor's Wife...
...So there's a case for such a massive change for the Doctor being used as punishment.
Yes, its been done before in a sense in the Unbound audio story Exile, Arabella Weir playing a future female Doctor whose change of gender comes about as a result of her previous Nicholas Briggs- voiced incarnation's suicide, which is evidently a punishable offence in the eyes of the Time Lords. But the result could change the fundamental nature of Doctor Who itself! 50 years of adventures in time & space as a man giving way to a brave new experiment in gender dynamics.
Sure, the idea of a female Doctor's had its critics- Peter Davison, aka the Fifth Doctor, among them. John Barrowman, or Captain Jack Harkness in another guise, is altogether keener-
"I think a female Doctor might work. You never know. The audience might not like that, but I know a lot of young girls and women would love that. Listen, if Captain Jack can be an omni-sexual time agent and assistant to the Doctor, why can't we have a female Doctor?"What a potential cliffhanger- the ( male) Doctor, having been found guilty of some offence, possibly a trumped-up charge, or even a justifiably, actually quite serious, offence should his personality have taken a turn towards darkness/malice, by the Time Lords once more- having finally found Gallifrey at the end of a long search. He enters a 'not guilty' plea, when the President enters proceedings! Only this time its nothing like The War Games.......& its not Rassilon who's the incumbent President. Its the Mistress, after a hell of a power struggle.........
And she's got her eye on a new form of ' restorative justice' for her old friend's latest abuse of his undoubted power. Once again he has no control over how he'll look in the aftermath of the change. One thing is certain though- she wants him to end up like her, to see how it feels. Perhaps his new personality will be one more like her own, & she'll have her old friend back. They always did share a sort of respect for one another.
In her own warped way, she might actually be trying to help him, restore him to a path more in keeping with the ' real' Doctor, the one she thought she knew all those years ago. It could also be a 'trial' for the audience too, could we accept a female Doctor? And could the Doctor learn to live with her sudden sex change after however many incarnations as a man?
One of the options presented to the Eighth Doctor prior to his regeneration into his War incarnation is to become female, thanks to the Sisterhood of Karn's potent potions. Perhaps that brew might have a part to play, whether punitively or otherwise. Back then he had to become a soldier, but the chance is still hanging in the air. One day we really might see a female Doctor at the TARDIS console! But what do you think? Do you prefer to stick with ' possible, it is' ( to quote the Sixth Doctor) & welcome the idea, or would you gladly add in a snide ' desirable, it isn't'? Plus, the potions offer the chance to make her a ' he' again.......
The Time Lords could also return her to her old gender by means of a remotely-induced regeneration once more at the culmination of the sentence if it were they who imposed it- after all they did give the Third Doctor his knowledge of space/time travel back post The Three Doctors, ending his exile to Earth in the process. They also granted the Eleventh a new cycle of regenerations as he neared the end of his life having used up his first thirteen - not such a gamble now, eh?