Okay Carly Smith / Rose Of Battle, I agree with you here for the most part. I don't like ethnicity swapping established characters in either direction. I also think this character being Japanese is a big part of both the character and the world setting. Take a lot of ethnic liberties with it or get politically correct and your just doing general transhumanist Cyberpunk, it won't be "Ghost In The Shell" anymore.
That said, who do you think should play the character? "Asian" is not an ethnicity and really this is very Japanese Centric. Consider also most "Asians" hate the Japanese, and the Japanese feel superior to them. One of the reasons why westerners are sometimes considered so racist is how we tend to lump all this together especially when we shouldn't. One example of this was how someone thought it would be a great idea to cast a Korean pop star called "Rain" as the lead in a movie called "Ninja Warrior" to much mockery. To a lot of Japanese this is like casting a monkey as a human (lower order of human, the Japanese are very racist) and the Koreans aren't exactly fond of The Japanese given that while it's not as famous as what Japan did to China, lots of abuse was thrown at them as well.
To properly do this character we need an ethnic Japanese girl with almost perfect looks, and in all likelihood a natural looking, but gravity defying boob job, who can at least pose for action scenes (they have stunt doubles and CGI for the actual stunts), AND can act. No offense but Rinko Kikuchi doesn't fit the role, and going by her one well loved appearance in Pacific Rim I don't know if she'd be good at anything else. Most Japanese Actresses I've seen who might fit the role tend to be the products of the craptastic Japanese movie industry where most of them can't act at all. Indeed a lack of good Japanese actors at all is one of the big reasons we haven't exactly seen many coming into the US. China on the other hand (not all Asians go together) does have a decent film industry and a lot of talented people, many of whom have managed to land roles in Hollywood movies due to talent. I'm sure exceptions exist, but for the most part when you think of Japanese Cinema your probably thinking of various horror movies, or action-horror-comedy flicks that rely on "WTF did I just see" gags. I've seen a lot of Japanese movies over the years and while names don't stick in my mind well I can't even come up with a "the girl from this movie might have been able to pull it off" kind of reference when it comes to filling this role.
That doesn't excuse ethnicity swapping, it just means I think the movie shouldn't be made unless they are going to do it right, and doing it right means they probably don't want to pay an "A list" actress anyway because done correctly this is very much the definition of niche science fiction. It's appeal is both in transhumanist navel gazing, and utterly insane futurist Japanese power fantasy. You remove those things and you've just got some generic action movie with a girl with super abilities beating people up. What's more to be fair while she establishes her credentials Major Kusanagi doesn't actually win all that many fights, half the time when it comes down to a fight she's already so overgunned by people ready for her that she needs help or gets taken down. Indeed the entire point of the character is for her to navel gaze over the nature of humanity before getting killed and being "reborn" in some impossible seeming, profound fashion that involves revelations about the technologies being used and what people thought their limits were. On some levels I think ScarJo would be wasted on the role, she's good at the action stuff, but that's only part of this role, and the lesser part. I'm not sure how well she'd carry philosophical navel gazing, overtly her Black Widow Schtick can come close to how Matoko acts outwardly most of the time, but that isn't where the gist of the story or how the character is defined.
That said I suppose from a Hollywood perspective ScarJo is a bankable resource with good name recognition, she's the action "It Girl" of the moment. They probably just want the "Ghost In The Shell" name to slap onto the movie and don't care about the soul of the IP. From their perspective ethnic controversy is probably good and it let's Hollywood claim it isn't just white characters being changed, they do it in reverse as well.... in the end it will probably make some short term bank over her name, and be a forgettable action movie, the animes and manga will probably see a short term spike in sales, and a few new fans for people who appreciate what it really is, but overall most who check out these things will be upset to find out it's nothing like the movie. Life goes on with another IP exploited for all it's worth by the current Hollywood machine.