I don't get the connection to WeChat here. You need to log in anyways, so why should WeChat run any fingerprinting? The user ID is right there, given by the user.
For context, some have argued [0] that modern Chinese life, in many ways, revolves around WeChat - chat, payments, location sharing, games, and more - and I don't find any reason to doubt those claims.
Sure, Apple could say no if WeChat decided to integrate fingerprint-driven tracking on iOS, but because of WeChat being a "super app" in China, Tencent could just say "sure, we'll stop supporting iOS" and that would cut iOS devices off from one of the most used apps in China, and make everyday life harder for everyone in China with an iPhone.
With iOS being the minority player in China [1][2], Tencent can likely get away with it too - I don't foresee a competitor rising up out of nowhere especially when WeChat still has a deep network effect for the remaining 78-82% of the population that uses Android.
[0]: obtained from Wikipedia: https://web.archive.org/web/20170103135948/https://www.fastc...
[1]: https://www.kantarworldpanel.com/global/smartphone-os-market...
[2]: https://gs.statcounter.com/os-market-share/mobile/china
I would somewhat disagree. Yes, iOS is a minority in China, but for wealthier people it's a higher percentage as it's a status symbol (as it is in many places). I don't know if this would change the calculus much but it might, and apparently the party is keen on cutting down on apps requiring more than essential data collection without consent[1] so it's possible that the government won't directly force Apple's hand in this case (as in, by forcing WeChat to remain in the App Store even using CAID).
1: https://www.reuters.com/article/us-china-cac-personaldata-id...
If any of those devices are sharing browsing history then that can be fused to online accounts. If any of those devices are active during daily commutes can fuse brick-and-mortar shopping destinations, place of employment, what daycare watches their kids, where Mom and Dad live.
Maybe, some of that data is embarrassing. Maybe, some of that data could be used to tell a story about you. Maybe, that story if false... but, would be very difficult to refute if made public. Maybe, you should just work with us (this one time, I promise) rather than have your whole life turned upside down...
No drop of water takes responsibility for the flood.