One thing I've always thought would be fun is an multi-Doctor episode with the current Doctor and the next Doctor. We've had the current Doctor with past Doctor's but never the future Doctor. The closest was Capaldi's eyes in Day of the Doctor.
That would be hard to pull off. But imagine running into a Doctor who is the next in line. The future Doctor references some mysterious/traumatic events, play up the mystery, and then we have to see how they get from that present point to the regeneration. I suppose at that point, the future Doctor would just be a guest star so perhaps not hard to keep a secret.
That would be hard to pull off. But imagine running into a Doctor who is the next in line. The future Doctor references some mysterious/traumatic events, play up the mystery, and then we have to see how they get from that present point to the regeneration. I suppose at that point, the future Doctor would just be a guest star so perhaps not hard to keep a secret.