I was just--I was listening, and going "you know, they never dealt with this. And it's supposed to be a future version." and then I tried to fit Eight or Nine or Ten in, and it just didn't really work (not as an insult, or anything, they just don't *fit* Merlin, if that makes sense). And then I thought "Oh, Eleven's all about puzzles and he's sort of Seven with less..." and it was a perfect idea.

Hrm. Juno Temple might work, yes. (I think she's got the gravitas to pull it off, if not quite the sharp, angular features)

Also, I briefly considered Amy being Morgaine, as in, Eleven manipulates her badly, and she snaps and becomes Morgaine (and while it is hilarious, it is a bad idea).