You know the only "what if" I have about John Wick is?

Wick, in the original script, was supposed to be a fairly innocuous looking older man.

Keanu, though, fell in love with it and helped the guys who directed it (stunt coordinators he knew from The Matrix movies) helped it get financed, and it probably wouldn't have been without him in the lead role.

Keanu is great in it, don't get me wrong, but I just kind of would have liked the whole "he's just an old man" thing turn into "Yeah, but he can still kill everyone in this room without breaking a sweat". Keanu is still young enough to seem threatening and formidable.

Similar casting "what if" I've always liked is that Tarantino's original choice for Donny "The Bear Jew" Donowitz was fucking Adam Sandler. I know that sounds ridiculous, but just think about that intro scene when Donny is coming out of the tunnel, smacking the Louisville Slugger against the wall, but instead of Eli Roth, out walks Adam Sandler.

Then, you'd wonder what real horrors this guy was capable of to earn such a fearsome reputation and nickname.