Shame, I wish I had more votes here, but the tendency seems to go for a 6-8 millions for China.
I also had an hypothesis, feel free to answer with agressivity this time if you think it deserves it but at least I will know if my thought are coherent or not.
I always believed that the XBOX1 was performing poorly in Japan, because many japanese did not want to buy the console from the console maker from the country who destroyed them in 1945... Will the Chinese people be attracted from the console maker, from the country who considered them as "slave stock" for centuries ?
The vast majority of people who live today don't care about what happened generations ago.
The Xbox One performed poorly in Japan because Microsoft had long established a negative reputation for the Xbox brand in Japan and doubled down on that with the XB1. The original Xbox barely offered any noteworthy games for the Japanese market, so it was of little interest for gamers (~500k lifetime). The negative perception carried over to the following console generation because Microsoft kept the same name; however, Microsoft made more of an effort to have appropriate games on the Xbox 360, so lifetime sales were notably higher (>1.5m). At around 2010 Microsoft had cut back on those efforts significantly and that mindset carried over to the Xbox One, so a sharp decline in sales was expected to begin with. The XB1 will finish with sales that are about 1/3 of what the original Xbox achieved and that's because it doesn't offer anything that can't be had on the PS4; the PS4 has everything the XB1 has, plus more.
Since Apple products have performed well in Japan, the assertion that the Japanese have a widespread inherent bias against American products doesn't hold water.
The Chinese won't shun Nintendo because Nintendo is Japanese. What will be important is how Switch will be distributed in China and how frequent game releases will be, and if Chinese gamers are open-minded to the different payment model of a console because the Chinese market is used to free-to-play. Since the questions about distribution will most likely be answered within the next week, there's no real point in throwing out wild guesses right now and speculate about lifetime sales.