Nationalism only works when there are divides, there aren't in Japan, I mean, there are no rules or law that discriminate Okinawan. This is what you don't know. Especially in unitary society, unless you are talkgin about Japan don't accept Okinawan as part of Japanese culture.
It's not easy at all to have someone to flip on where their own government. Especially in East Asia, it's not at all an easy way, because, there are always balance in the system.
And WW2 is 80 years ago, if there were ANY independence movement, you would already been seeing it. The "resentment" are there, but I would say Chinese resentment over Japanese government is even greater than the Okinawan.
As I said, you can't even tell me what's the play for China, and yet you still think this is going to succeed 50 or 100 years down the road? I can tell you this, in a stable society, resentment goes down over time, even if you are talking about oppression of native population like US did to the Indians and Australian done to aboriginal. In a balanced society, the crack will grow smaller and smaller as time goes by, which mean you would have less chance to get separated as times goes on.
I am talk about that, sure, but actually thinking this is easy, is another matter.