Rambling coming. Sorry, no turning it off now.
Not quite on target, but geez, every time Dragon Ball Evolution gets brought up all I can do is shake my head. First because it's god-awful, but then because the argument about "White Goku = Muh Cultural Appropriation" is about as short-sighted as claiming that Kurosawa's Ran is an insult to King Lear. Does anyone who uses that as an example even bother doing a head-count? Five of the main cast members are Asian actors, only one of whom is a particularly established name (Chow Yun-Fat). The director is Asian, as well, for what that's worth.
Plus, the two main characters are - canonically speaking, at least - literal aliens from outer space. One of them spends the entire movie in... screw it, let's call it "greenface". They also changed his outfit to avoid looking like a historical Persian stereotype, because if there's one thing creator Akira Toriyama's really good at, it's extremely shallow stereotypes - see Mr. Popo, Mr. Satan and Tao Pai-Pai for a handful of obvious examples. I don't think they're malicious, mind you, just pretty far outside what would be considered racially or culturally sensitive.
Yes, the "main" character in DBE was a generic white kid - so what? We've already seen what an all-Asian version of Dragon Ball looks like, because Taiwan made a movie called Dragon Ball: The Magic Begins in 1991. It's an unlicensed adaptation, but that's... pretty common with non-Japanese East Asian anime and adaptations from the early 90s. (As for the movie itself? Let's just say Goku being played by an Asian doesn't fix much. I won't deny that it has a certain Power Rangers level lo-fi charm, but calling it "good" would be a stretch...)
Back to Ghost in the Shell. Honest question to Carly here: Have you read the original Masamune Shirow comics, or just seen the Mamoru Oshii movie adaptation? Because [INSERT SPOILER WARNING HERE] while the movie ends with Motoko's body being "replaced" with essentially a younger version of herself, the manga ends with Motoko being inserted into a male shell - much to the shock of Batou, who simply grabbed what he could. The very DNA - and in fact the whole bloody point of the Puppet Master storyline featured in the '95 film - is to question the notion of "self" in a world where one's self is simply a consciousness that can be placed into any shell, even an inhuman one, or a consciousness that has no body to claim as its own.[/DONE SPOILING NOW, PROBABLY]
Basically, the origins of the character are fuzzy enough that she could be anyone, and the core idea of the franchise - particularly the Stand Alone Complex TV series - is that the notion of "identity" aren't as clear-cut as society seems to think of them when the possibility of changing bodies becomes possible. The Oshii film suggests she actively doesn't care about her body, and a big element of the film - which is substantially less at the forefront of the other versions, as I remember it - is that she seems to have fallen out of touch with seeing the body she's in as "herself". In short, Motoko can look like anyone, and has proven she no qualms about using a separate body to accomplish her goals. Scarlett Johansen being cast isn't an issue because she's Caucasian, because the racial identity of an isolated consciousness isn't inherently tied to the strands of its DNA that dictated its skin color.
Mind you, this doesn't always work. Akira - at a meta level, at least - is a frustrated reflection of the societal shock that happened to Japan after the end of WWII, and specifically the atomic bombings of Hiroshima and Nagasaki. Randomly setting that in "New New York" or whatever changes a lot of the political and cultural baggage that's inert to the whole point of the story, that the 'end of the world' is only as good or as bad as those who find themselves left behind choose to make it. Could you recontextualize that for a Western palette? I guess so, but that would basically undermine the whole point, unless you really think spending a fortune on the rights to the badass red bike and pill-jacket combo are worth the price.
This discussion swings both ways, too - even if the "more minorities = more diversity" argument is brought up, particularly when, as others have already pointed out, several groups are over-represented by a pretty wide margin. (Not that I care either way, just stating facts as they exist.) The upcoming Japanese movies based on Attack on Titan take place in a world that's inspired by Germanic folklore, and there's an in-universe discussion about how Mikasa Ackerman is presumed to be the last ethnic (half) Asian in existence. So, what does the movie do? Creates a new cast of similar archetypes in a different part of the universe that are all ethnically Japanese. Problem solved, right? Sure... except for the fact that Eren Jaeger and Armin Armout show up. These are characters who are explicitly stated to be non-Asian, and are, naturally, played by Japanese actors with blonde hair. Because that isn't stupid or anything...
So, you want to talk about casting Asians and setting the story in Japan when it's Akira? You've probably got a solid point. You want to bring it up in GITS? Not really seeing the problem here. I mean, yes, there could be huge problems, but setting it in Washington, or France, or Belize wouldn't be the inherent stumbling block for this particular project.
Besides, if the only stipulation is that an actor be "Asian", that's kind of... well, it's just a little weird to me. It made sense before I watched a lot of Asian films - Japanese, Korean, Thai, Hong Kong - and realized just how different Asian films can be, linguistically and culturally. But if the argument is solely down to looking the part, Japanese and Korean features tend to be pretty similar, but Thai and Malaysian look quite a bit different. What about someone like Keanu Reeves - Theodore Logan is half Hawaiian-Chinese. Does he qualify as "Asian Enough" for movies like 47 Ronin? And should we give Valkyrie guff for casting a non-German as a Nazi? Or is getting cultures miss-matched okay so long as they're all still white... I'm not a terribly PC person, I suppose, so the whole thing confuses me.
(For the record, I could care less that Idris Alba is a Norse God. No, it doesn't make much sense for a seemingly otherwise mono-ethnic race of aliens whom inspired the images of Norse mythology to have one black guy... but dude. He's Idris F'ing Alba. Cast him as Christ next time, please.)
But the bigger issue here is that there's simply no Asian-American actresses worth banking an entire production on. You could grab one of the successful actresses from Asia - Ziyi Zhang and Michelle Yeoh might have a little star power in Hollywood at this point, but outside of Rinko Kikuchi I can't think of a single Japanese actress that could draw a non-Japanese audience by recognition alone. And let's not forget that for how friggin' amazing Pacific Rim was, it under-performed at the US box office. The only Asian-American actress I can think of with any level of legit mainstream appeal is Lucy Liu, and that was... quite a while ago, now that I think of it. Are Asian actors in Hollywood denied better roles because there isn't a market for them? You bet. How do you fix that short of mandatory affirmative-action style quotas, which are obviously BS? I don't really know. Popular Asian actors exist in Asia, but even then, they rarely get the sort of cross-over appeal when they come to Hollywood. Can anyone name one Asian actor with a notable presence in the last 15 years or so? I'm legitimately curious, because short of going for Ziyi Zhang or Tony Jaa (who's not even an actor!), I can't think of any off the top of my head.
And just to remind people that "cyberpunk" is still pretty niche, the closest film to GITS in recent memory - Automata - basically got crapped out straight to on-demand. And that was with Antonio Banderas in the lead. Again, not 1995 Antonio Banderas, but if this project put even a bankable Asian actress in the lead, I would assume it'd get the same sort of promotion.
For the record, the only actress I'd have picked for this role is Noomi Rapace. She could do the "dead eyes, agressive body language" thing Oshii perfected in her sleep. I have nothing against Scarlett, but about all I've seen her in is The Avengers and Lucy, neither of which make a particular case for the cold, detached personality required (unless they want to go back to the smarmy, pulpy tone of Shirow's books, which seems doubtful). That said, I've heard nothing but good things about her in Under the Skin, so it's entirely possible she could surprise me for the better under proper direction.
Make no mistake, I'm expecting I'll hate this movie's guts - assuming it even happens. But in this particular case, the fact that a pretty white lady is playing a pretty Japanese-named cyborg is the least of my worries.