Ay, The sad thing is, Hollywood is a business. It affects a lot of things. Mickey Rourke is a well known quantity, even more so now when he played the villain in Iron Man 2 which was a blockbuster so his name alone will
generate revenue, kinda like Christopher Nolan for the new Superman movie.
On that note though it's not only minority actors that are getting the shaft from hollywood, VFX houses have been getting screwed recently, and most work is done overseas for little pay. So for us westerners, it's a lot harder to get work in this industry and don't get me started on the gaming industry.
On topic though, Tonto for sure. Khan is defined by his superior intellect and ruthless brutality, rather then his racial origins, which is what Star Trek tries to tell us. It's not the race/gender/sexual orientation, it's all the other stuff underneath. The soul of a human being; our flaws, our strengths, and our motivations is what make us truly unique.
Johnny Depp playing Tonto, is just another loose impersonation of Silly Depp cause he's a hit with the Disney audience/demographic. Don't get me wrong though, Johnny Depp is a great actor if not one of the best, he just likes doing kid movies for his kids.