They are not expanding the setting, they are changing it to accommodate new ideas. They're not advancing the timeline to expand options and improve diversity, they're retroactively rewriting it. I don't object to cultural sensitivity (thanks for the shot, by the way), I object to changing history. If they feel the original setting is no longer appropriate in 2022, retire it and make a new "Oriental Adventures" setting. Don't pretend things have always been better. Make a better world.
Of course that is hogwash if you are talking about it being historically accurate to Feudal or even 16th - 19th century Japan. If I understand the setting right, they allow Gay Marriage. That is NOT something that was allowed then, and is a modern invention of our times. In fact, that they allow many various things along that manner in a way that is absolutely NOT historically accurate should say all one needs to know about the historical accuracy of the setting.
It isn't.
Is the game have you able to play all various types of different character races like naga, or ratfolk? WELL, it may be based on a mythological take of Japan, but then you have all sorts of ideas (with PC's being the heros) of characters that would have NEVER been heroic in Japanese mythology, and in fact could be seen to make a mockery of Japanese Mythology? Is it a historical accurate representation of Japanese Mythology. That it takes things that would never happen in Japanese mythology probably says what you need about how accurate it is to Japanese Mythology.
It isn't.
It takes SOME tropes from Japanese mythology (the idea that all samurai were based upon a samurai code...yeah...that didn't happen historically. They played dirty politics just like many other cultures, and the ones who played it dirtiest sometimes came out on top. That idea that they all lived the code to it's highest ideals is a completely mythological idea, sort of like the idea that all european medieval knights lived chivalry and were chivalric and gallant to the highest ideals. Obviously they weren't.), but it isn't in any way of fashion accurate to historical Japan or mythological Japan.
It's a fantasy setting with similarities to Japan.
In that instance, they can do whatever they want with the setting. It isn't the real world.
I haven't read the book yet, don't even have it, so I don't know how bad these changes may or may not be.
However, from what I've read about it, this book seems to be going for a broader appeal to gamers than the L5R game, and as such has made broader changes that appeal more to the casual or even dedicated 5e D&D gaming base.
It sounds like it is more akin to what 3e OA was rather than what L5R has become. As a D&D player, that's probably more of what I WOULD want. I haven't been all that interested in the L5R mechanics. I've never really gotten invested in them. The most has been with the 3e OA and Rokugan books.
I AM interested in this book though, and with it's integration into 5e. I'm probably the target audience for this book.
Of course, the BIG question I would like answered is how many actual Japanese, Chinese, and other individuals from those nations actually had input in the book. I'm not talking AMERICAN Japanese or Chinese (as some of them have EXTREMLY OFFENSIVE IDEAS related to those who actually live there these days, and as they are really AMERICANS with the Japanese, Korean, or Chinese or other Asian heritage, and NOT really from those nations, though they can speak and have their input, and it's more valuable than none at all, I'm interested in how much input those from the actual nations they are taking cultural ideas from have in the book itself). I know the original OA at least had some from the Japanese culture that had input, and other books have had it, but I have no idea how much input they currently get form individuals who are born and live in the actual cultures of the lands they are taking these ideas from (Japan, China, Korea, East Asia...etc) (and L5R for that matter).
That said, I AM highly interested in the book, and it looks like something I would enjoy reading.