If they ban Xiaomi, OPPO and Vivo, they would hope that all Android smartphones will be made by Samsung. Even Google Pixel, LG, Nokia and Sony will resurge in the business.They would never pull this move because Xiaomi is what is keeping Qualcomm in the mobile soc market. Apple and Samsung use their own custom chips and it would really hurt the Americans as much as it hurt Xiaomi.
If you think about it, America with her recent actions has lost the leverage it had. It has now become a symbiotic relationship.
Google now depends on a few Chinese hardware companies to distribute Android.
The Huawei ban has now left the US with a strategic vulnerability. It only worked because there were other Chinese companies that would replace Huawei. You ban Xiaomi, OPPO and Vivo and suddenly, Google and Qualcomm can't reach the consumer.
You'd be talking about huge massive phone shortages across the world because no other country can rump up production like China.
You'd also have 4 experienced Chinese companies determined to dethrone Google on the software side.