Probably better just relocating labor intensive parts of the Chinese economy to Pakistani especially if the products are going to or raw materials are coming from Africa or the Middle East. Similar to how Japan has build factories in ASEAN countries/Bangladesh/India and decreasing the need to import labor, shifting part of the production to a large and friendly lower labor cost country is a win win solution. Pakistan will earn more money to spend on more Chinese procure to build up more of its industries and buy more Chinese goods.
Considering the 996 expectations, many Pakistanis probably wouldn’t want to work in China based factories itself. Many Pakistani don’t want to relocate to other cities in Pakistan for manual work, much less other countries. The white collar workers and Students are a different story and would probably be more willing to move to advance their careers.
This is why a direct rail line between the two countries would be truly game changing (costing under $25 Billion). No need to depend on the Afghans and Central Asians (potential interference from the Russians, Turks, and Western countries), and its benefit to China as an alternative to sailing supplies around the Indian Ocean and south east Asia are benefits to Chinese business.
If you imaging Pakistan similar to the West coast of North America with the mountains in between the two countries like the American Rocky Mountains and China itself like the eastern 2/3 of North America, you can see this will effectively for Chinese business make the China’s logistical opportunities similar to the US and it’s two ocean routes.
Migrations, even if allowed, may result in a few million Pakistanis moving to China, but a shift of industries to Pakistan allows these factories to pick the best talent from amongst nearly the entire labor force