We have less than 8 billion people on the world which corresponds to about 2^33. Let's assume that (given that we already have issues with sustainability) we wi

We have less than 8 billion people on the world which corresponds to about 2^33. Let's assume that (given that we already have issues with sustainability) we will have much bigger issues than IP addresses if we ever reach more than 128 times that. So we are at less than 2^40. (Realistically I would expect much less, but let's be safe) Than the question is how many addresses everyone needs. Currently we assign subnets. Let's provide everyone with 1024 subnets for client devices and an additional 1024 servers each with their own subnets. So 2^11 subnets each. So we end up requiring 2^51 subnets, while we have 2^64 available, thereby only using less than 0.013% which provides plenty of room to reconsider if any of these approximations turn out to be wrong.