Presumably the villain if the piece would be Firefly?
It just occurred to me, the Firefly cast, plus assorted Whedon alumni, might not work for a film. But if there was a new Batman TV series....
Also, Nathan could
work as Batman, depending on the tone of the piece. A dark and gritty version....no chance. But something action packed and fun, clever and witty, not quite tongue in cheek, with just a hint of self awareness...he'd be ideal for the role.