This already happened years ago since for many years China hasn't had "majority of hashrate". I speculate that only about 20% of the hashrate is currently located in China, the rest is spread across the globe. Unfortunately people usually confuse "mining pool" (which a server that miners coming from all around the world can connect to) with "mining farm" (which is actual hashrate). There are multiple mining "pools" owned by Chinese that have majority of hashrate among them but there aren't enough mining farms in China to get "majorith of hasharate".
I appreciate your excellent point. Mining pool is just brand new and I can connect my rigs to any mining pool I want, if they don't restrict my national IP. Unfortunately, because there is no way to get exact numbers, and no public and transparent report about it, people only guess and believe that most of hashrate is in China. They believe so because China is a biggest manufacturing location of the world and also for ASICs.
They have reasons to believe so.