I saw the Misha Collins thing. Never heard of the guy and apparently he's prone to Twitter jokes. Plus he's not British, which would cause a massive Anglo-aneurysm on Sunday if it's him.
"How dare they cast a Yank ZOMG the world is gonna end I wanna kill myself they've ruined an iconic British show by pandering to the Americans enough already UGGHHHHHH I am so done BBRZZZZWWWPPsssh....! *die*"
And the live audience would boo.
Nah. It's not him.