Hate to disagree with you, but according to that logic, people can just move to China, and if they act sufficiently Chinese, then they should get a Chinese citizenship.
That's not how it works, is it though?
There was a real move toward recognizing dual citizenship some 15 years ago, but unfortunately it was scuttled by the increasingly hostile attitude of Western countries against China.
The definition of Chinese varies.
Is it cultural?
Is it geographical?
Is it racial?
Note religion isn't a big factor.
Being Chinese is kind of like saying you're a Westerner. As in from Western Civilisation.
What seems to have happened throughout history is that the definition of Chinese expands when time are good and China is confident.
And when times are bad, it shrinks back to a core racial and geographical area.
But nowadays, China itself is becoming more homogenous as minorities are being assimilated into mainstream Han culture.
So the definition of a Chinese citizen is mostly geographical as race/culture are becoming less of an issue.
And in the future, I think China will be confident enough to accept naturalised immigrants, knowing that they will end up adopting Chinese culture. I think Singapore has a very good model (the world's best?) for immigration, naturalisation and assimilation.