Great video, nice to get some more info on how it all works under the hood.
I gotta say though, with the whole extension methods system.. Why not just add a keyword to the function declaration rather than an oddly placed 'this'? Like: public static extension void Foo(Class c, ....), possibly omitting the 'static' (they're always static). It's much easier to spot not to mention more intuitive, at least to me.