5. Ridley Scott
OK, so Prometheus might have divided fans but nobody does Sci-Fi like Ridley Scott. With the rumoured Blade Runner Sequel becoming more and more likely, as with Whedon, it might be a stretch getting Scott to commit to such a huge production. There is also the issue with George Lucas. Scott has been very critical of 5 of the movies in the series with only the original Episode 4 receiving his praise. Disney will definitely want a family friendly franchise and Scott might not adhere to toning down his vision.