3. He Could Play Multiple Parts
William Hartnell did it as the Abbot of Amboise, Patrick Troughton did it as Salamander, Tom Baker did it as Meglos & Matt Smith did it as Mr Clever/ the Cyber-Planner. And nobody says this Doctor couldn't do similar. He's probably most comfortable playing himself though, which is fine for now. Imagine his Doctor meeting his real life self, though, and just feel your brain starting to melt a little. Would Doctor Brian and Real Brian get along, though, or would they engage in an epic mental duel? Questions like that often show just why these sorts of episode have been made before, but having the seemingly nice Cox become something else entirely would weed out the dedicated fans from the ladies who only watch his usual output because he's all cute & nice & stuff. The fact he knows a bit might not enter into it by that logic, and it's almost worth doing for the look on the fairweather fan's face as he really hams it up.