Anyone who knows anything about Lucas' artistic roots would know why he dislikes directing studio films but still directed the prequels. It's easy to google.
I don't get the cheerleading/love for Vaughn, but think Bird is a good choice, with Whedon on board for writing duties.
Just to add another name in the mix: Peter Berg. Decent action/sf director.
Would love to see Horner or Debney get a crack at the score.