The general priorities in lives of people in China and other East Asians, (excluding Indonesian Muslims, Malaysian Muslims and Philippines Christians) are
1. Personal finance, i.e. jobs and business
2, 3 & 4. Housing, Children's educations, social life styles
5. Traditional cultures
Religion is low down on priority lists not only in China, but also among many people in East Asia and South East Asia, excluding Muslims and dedicated Christians.
Muslims treat their religion as top priority above everything else including their lives, thus the potential conflict of social, culture and religion between Muslim/ religious Christian immigrants and Chinese is very real if both sides do not understand and cannot tolerate their differences.
And asking Muslims immigrants to forgo their religious practices and belief in the land of atheist can have very undesirable consequences.
Example of religious rebellions in China:-
Quanzhou city in Fujian once had a very large Persian and Arabic Muslim population from Middle East, Quanzhou even had an Arabic name called Zaiton city. And from 1357 to 1366 Muslims in Quanzhou participated in the Ispah Rebellion, advancing northward and even capturing Putian and Fuzhou (provincial capital) before the rebellion was crushed by the Yuan government.
Also there is the famous Taiping revolution (1850-1864) lead by Christians that almost defeated the Qing government.
Conclusion, Pakistan is certainly not the solution to China's demographics problem.