The little voice in my head goes "Really? After his runs on Astonishing X-men and Runaways? At this point, they can clearly afford Russell Mallachy..."
Sorry, I just don't think that Whedon's style is suited to feature-length projects and his writing runs with Marvel were just "okay". Depending on the feel they want to go for, if they want action and to ham it up a bit, I'd say go with Mullachy. For a moodier tone but still lots of action, probably Christophe Gans (Brotherhood of the Wolf was excellent, I've not seen Silent Hill) or Timur Bekmambetov.