Yes but how would China integrate so many people?
It would need to ensure that these people know Chinese, same cultural values (SEAsians), CPC authority, forget their Democratic values, stop them from getting influenced from foreign influence operations etc.
Honestly, its a lot of trouble. I cant imagine immigration coming from any other region than SEA. And even then there are still dozens of issues and problems in order to ensure a safe and functional immigrant population.
Thats why I emphasise forming a consensus among the society before starting it as it would seriously strain local resources and increase competition to their areas which would inevitably lead to discontent among the local population.
This already happens with rural workers going to urban regions and they face discontent and some opposition from the locals there. Can you imagine if you also put some foreigners there..
TBH, any potential immigration to China would likely be to tier 1 and tier 2 cities, not middle of nowhere. While Han make up 90% of population in China, its even higher in those cities so they are more easily absorbed into the new chinese culture than if they went elsewhere. As china further urbanizes its heartland over the next 10, the remaining rural population will likely be older people who naturally are less pressured to emigrate to cities. While income inequality may persist between countryside and cities, its more likely that the tensions of migrant workers will recede as this pool becomes smaller.