1. Rupert Grint
Take a moment to get the giggles out, kids. I know, I know. That sounds like a ridiculous choice for the Master, but wait! Remember my earlier theory, which is actually science, about actors proving their range by playing crazy people? Well what better way for this famously innocuous ginger to break the mold and play a famously nocuous one? The Master. We're working entirely in hypothetical here, but let yourself embrace a kind of change you're not accustomed to. Sometimes, what seems like terrible casting turns out to be the best part of the film or show. And how much fun would it be to pit an older, more seasoned Doctor against a younger, more wild and mischievous Master? Though it's been the cause of much fan fervor, think of it like Jesse Eisenberg as Lex Luther. It's an off the wall choice that inspires initial reactions like, "What?", "Why God?", "Lame", and my favorite, "You ruined my childhood." Grint is the sort of random, weird, absurd choice that, when you think about it, might make a great fit for a weird and absurd character. If you disagree and I've just lost all credibility in your eyes and you're never going to read another article of mine again, I'm anticipating your inevitable outrage in the comments section below.