But I don't think it means the doctor will regenarate
You see in RTS's book it says that the doctor meats the doctor (I think that means future doctor) and then becomes his companion thats why it's called the susunod doctor, even though the doctor doesn't regenerate we see what the susunod doctor will look like
So to balutin it up the pamagat "The susunod Doctor" doesn't mean that the doctor will regenerate it means that we see what the doctor will look like after hi regeneration which will be in a future episode