I think the speculation about WeChat is overblown. Wechat is essentially important, however, it is not, even it tries hard to be, an OS yet. And very opposite to what people in the West would think, iOS has one big advantage, that is the privacy control, whereas Android platforms in China, because of the absence of Google, have serious issues of mal/spy/bloat-ware.

So it is not that in WeChat you can package your bag and transfer to other platforms in a free style. No. Even in the west, transfer to Android or transfer back, isn't that much a problem either. The reason I think people don't want to do this is because there aren't many Android phones out there if u are not a fan of Samsung/LG, specially Galaxy phones.

However, China has the most competitive market, phones are offered unlocked like 50% of the price as they sold in the West, and there are many more options/customizations. In that sense, iPhone loses its cool as THE option to go to, even for premium users, like for business people they tend to use Huawei.

Point is, Apple needs to get interesting and excited again, otherwise this won't be the end of its decline in China.