If you choose a 32-bit integer for your PK it can only address about ~4 billion records. That was true 1000 years ago, and will be true forever until a black hole swallows everything and changes the laws of reality.
Forget how many angels can dance on the head of a pin, the real question is can God change the value of pi, or can God make 32 bit integers larger than our current max? In both cases what it means to math is more Interesting than any yes/no.
Once day I got into work and a slightly panicky dev said "We need to change the primary key on all the tables"
It was using an int and at the current rate of data entry, was going to blow the maximum record number in a couple of days.