"kbarros" identified this issue.
To cast a method to a specific callable type, right now we can only use cast() or implicit casts. As casts always fail. Example below. I attached a patch that I hope is the right way to allow as casts to work.
callable OutputHandler(message as string)
def printit(message as string):
handler as OutputHandler = printit
//doesn't work, null ref exception
handlerb = printit as OutputHandler