Mad Man's Words

The only way I accept Tennant and Piper back is if whenever there's more show, it's three specials and Piper steps out of the Regeneration energy but the Regeneration energy itself is still there as a scar in time, vaguely in the shape of how Gatwa was standing

And Piper looks at it, scans it with the Sonic and then strangely just - ignores it. She shifts the TARDIS spatially to confirm it's locked to location and not the TARDIS and then leaves (note, the positioning of Joy can serve as an establishing location for later)

Then she has an adventure with the Daleks that very much has Eccleston Dalek tones where the Doctor is angry and dark, but the audience gets it - these are Daleks. There are hints of Susan during it, though - all on screens, but with a visible facial tick from Piper. The episode ends with us seeing Susan on a TARDIS screen and Piper doesn't look at it or even seem to notice it, but does flip a switch in time with the screen changing.

Special 2 is when Tennant comes in. He's very much seeking out the Doctor. He finds her and reveals that his TARDIS was giving him critical warnings that made him think he was needed and the other Doctor was in danger and there's something they need to handle. Crucially, he doesn't even mention the face - he knows immediately that it's the Doctor and doesn't think it's his place to explore WHY it's the Doctor. They go off in Piper's TARDIS and there's a Multi-Doctor adventure with a new enemy. At some point, they get split up. Piper is making choices more like how Gatwa FUCKING TORTURED A GUY and while that's happening, we do cut to what Tennant's doing and he gets mental messages from Susan telling him to stop what the Piper Doctor is doing.

He stops her from going too far and they both together resolve the alien nonsense. In the TARDIS, they argue with Tennant lecturing about not going too far.

"You're one to talk - Time Lord Victorious" "That was this face, but that was not this Us. And he's just as much in you as he is in me. And we were wrong back then. I know it. Why don't you?" "Were we? There's so many monsters we face and they never end. We should just end them." "They're not monsters - they're living beings. How can you be so cold hearted?" "There is ice in my heart now that may always be there."

Tennant notes the singular nature of "heart" and then scans her to reveal she only has one heart.

Piper kicks Tennant out by bringing him back to his TARDIS. The special ends with Tennant getting another "Grandfather! Find me!" from Susan.

Special 3 is as long as it needs to be - not constrained to 45 or 50 minutes. Could be 90 minutes if they have the narrative to support it. It has 14 finding Susan. Interspersed are scenes of some Piper Doctor adventure where she's holding nothing back at all. They converge with Susan and 14 trying to stop the Piper Doctor from doing something atrocious and they fail.

"How can you justify this? How can you think it's right?" "Have you really not seen this face? We both know who I am. I'm the big, bad wolf. I'm allowed to have a bite." "Don't you dare pretend that's who she was. The Bad Wolf helped us save lives - she made it possible for us to save Gallifrey from the Time War. And Rose --" "If I'm not Bad Wolf then what am I?" "What you told me you are not too long ago - me, with ice in your heart. [Beat] Or what you told me so long ago in the courtroom. Do you remember?" "Do I - No. What courtroom?" "It's your future. I used to think it was ours -- but we never remember our future. Timelines out of sync. Always wondered why I remembered you."

14 stops Piper from doing something even worse and then she escapes in her TARDIS. If they feel it's necessary, Tennant can exposition dump to Susan about Trial of the Timelord. Getting ahead- the credits list The Valeyard - Billie Piper.

The special ends with 14 bringing his TARDIS to the Regeneration scar - establishing shot of the Joy star before we see inside the TARDIS with the regeneration energy in the exact position Gatwa left it in.

Then there's two options I see:

First is have 14 lean into the position and then transition into Gatwa with the regeneration footage they already have and then the actual 16th Doctor.

Second is for 14 to say "Not a moment too soon. I've said my piece long ago - you were there. I'll leave this next bit to you."

And he leans in and regenerates into 15, but the hands give it away that the process isn't over (as usual). Bring in Gatwa for a day to film another regeneration scene. He comments about having one heart now and says "That should sort itself out in a Regeneration or two" and has some other lines before regenerating at the console into the proper 16th Doctor

inspired by this post by @the-macra:

It's rude. You're making someone take their time to read something you couldn't bother to write. You're telling them they were so unimportant you couldn't be bothered to actually take the time to say something yourself. And frankly, you're lying about it while you're at it.